IPv6 causes Duplicati to fail with connection refused (lp:#1405705)

[Original report](https://bugs.launchpad.net/bugs/1405705) created by **Ricky-burg (ricky-burg)**
```
Duplicity version: 0.6.24-4.fc21
Python version: 2.7.8-7.fc21

With IPv6 and IPv4 hostname:

[rburgin@Ricky-PC ~]$ duplicity -v9 full /home/rburgin/Documents
scp://duplicity@private.orbixx.com/Documents
Using archive dir:
/home/rburgin/.cache/duplicity/79ed15f54c43bfd4b8bb0c0c229c5f47
Using backup name: 79ed15f54c43bfd4b8bb0c0c229c5f47
Import of duplicity.backends.botobackend Succeeded
Import of duplicity.backends.cfbackend Succeeded
Import of duplicity.backends.dpbxbackend Succeeded
Import of duplicity.backends.ftpbackend Succeeded
Import of duplicity.backends.ftpsbackend Succeeded
Import of duplicity.backends.gdocsbackend Succeeded
Import of duplicity.backends.hsibackend Succeeded
Import of duplicity.backends.imapbackend Succeeded
Import of duplicity.backends.localbackend Succeeded
Import of duplicity.backends.megabackend Succeeded
Import of duplicity.backends.rsyncbackend Succeeded
Import of duplicity.backends.sshbackend Succeeded
Import of duplicity.backends.swiftbackend Succeeded
Import of duplicity.backends.tahoebackend Succeeded
Import of duplicity.backends.webdavbackend Succeeded
Import of duplicity.backends.~par2wrapperbackend Succeeded
Using temporary directory /tmp/duplicity-N2Bbih-tempdir
Backend error detail: Traceback (most recent call last):
  File "/usr/bin/duplicity", line 1502, in <module>
    with_tempdir(main)
  File "/usr/bin/duplicity", line 1496, in with_tempdir
    fn()
  File "/usr/bin/duplicity", line 1329, in main
    action = commandline.ProcessCommandLine(sys.argv[1:])
  File "/usr/lib64/python2.7/site-packages/duplicity/commandline.py", line
1059, in ProcessCommandLine
    backup, local_pathname = set_backend(args[0], args[1])
  File "/usr/lib64/python2.7/site-packages/duplicity/commandline.py", line
952, in set_backend
    globals.backend = backend.get_backend(bend)
  File "/usr/lib64/python2.7/site-packages/duplicity/backend.py", line 163,
in get_backend
    return _backends[pu.scheme](pu)
  File "/usr/lib64/python2.7/site-
packages/duplicity/backends/_ssh_paramiko.py", line 219, in __init__
    self.config['port'],e))
BackendException: ssh connection to duplicity@private.orbixx.com:22 failed:
[Errno 111] Connection refused

BackendException: ssh connection to duplicity@private.orbixx.com:22 failed:
[Errno 111] Connection refused

With IPv4 (same host):

[rburgin@Ricky-PC ~]$ duplicity -v9 full /home/rburgin/Documents
ssh://duplicity@78.143.255.136/Documents
Using archive dir:
/home/rburgin/.cache/duplicity/2ce2771e0b9865a5d162e53ca22a5987
Using backup name: 2ce2771e0b9865a5d162e53ca22a5987
Import of duplicity.backends.botobackend Succeeded
Import of duplicity.backends.cfbackend Succeeded
Import of duplicity.backends.dpbxbackend Succeeded
Import of duplicity.backends.ftpbackend Succeeded
Import of duplicity.backends.ftpsbackend Succeeded
Import of duplicity.backends.gdocsbackend Succeeded
Import of duplicity.backends.hsibackend Succeeded
Import of duplicity.backends.imapbackend Succeeded
Import of duplicity.backends.localbackend Succeeded
Import of duplicity.backends.megabackend Succeeded
Import of duplicity.backends.rsyncbackend Succeeded
Import of duplicity.backends.sshbackend Succeeded
Import of duplicity.backends.swiftbackend Succeeded
Import of duplicity.backends.tahoebackend Succeeded
Import of duplicity.backends.webdavbackend Succeeded
Import of duplicity.backends.~par2wrapperbackend Succeeded
ssh: starting thread (client mode): 0xb0b16f10L
ssh: Connected (version 2.0, client OpenSSH_6.4)
ssh: kex algos:[u'ecdh-sha2-nistp256', u'ecdh-sha2-nistp384', u'ecdh-
sha2-nistp521', u'diffie-hellman-group-exchange-sha256', u'diffie-hellman-
group-exchange-sha1', u'diffie-hellman-group14-sha1', u'diffie-hellman-
group1-sha1'] server key:[u'ssh-rsa', u'ecdsa-sha2-nistp256'] client
encrypt:[u'aes128-ctr', u'aes192-ctr', u'aes256-ctr', u'arcfour256',
u'arcfour128', u'aes128-gcm@openssh.com', u'aes256-gcm@openssh.com',
u'aes128-cbc', u'3des-cbc', u'blowfish-cbc', u'cast128-cbc', u'aes192-cbc',
u'aes256-cbc', u'arcfour', u'rijndael-cbc@lysator.liu.se'] server
encrypt:[u'aes128-ctr', u'aes192-ctr', u'aes256-ctr', u'arcfour256',
u'arcfour128', u'aes128-gcm@openssh.com', u'aes256-gcm@openssh.com',
u'aes128-cbc', u'3des-cbc', u'blowfish-cbc', u'cast128-cbc', u'aes192-cbc',
u'aes256-cbc', u'arcfour', u'rijndael-cbc@lysator.liu.se'] client
mac:[u'hmac-md5-etm@openssh.com', u'hmac-sha1-etm@openssh.com',
u'umac-64-etm@openssh.com', u'umac-128-etm@openssh.com', u'hmac-
sha2-256-etm@openssh.com', u'hmac-sha2-512-etm@openssh.com', u'hmac-
ripemd160-etm@openssh.com', u'hmac-sha1-96-etm@openssh.com', u'hmac-
md5-96-etm@openssh.com', u'hmac-md5', u'hmac-sha1', u'umac-64@openssh.com',
u'umac-128@openssh.com', u'hmac-sha2-256', u'hmac-sha2-512', u'hmac-
ripemd160', u'hmac-ripemd160@openssh.com', u'hmac-sha1-96', u'hmac-md5-96']
server mac:[u'hmac-md5-etm@openssh.com', u'hmac-sha1-etm@openssh.com',
u'umac-64-etm@openssh.com', u'umac-128-etm@openssh.com', u'hmac-
sha2-256-etm@openssh.com', u'hmac-sha2-512-etm@openssh.com', u'hmac-
ripemd160-etm@openssh.com', u'hmac-sha1-96-etm@openssh.com', u'hmac-
md5-96-etm@openssh.com', u'hmac-md5', u'hmac-sha1', u'umac-64@openssh.com',
u'umac-128@openssh.com', u'hmac-sha2-256', u'hmac-sha2-512', u'hmac-
ripemd160', u'hmac-ripemd160@openssh.com', u'hmac-sha1-96', u'hmac-md5-96']
client compress:[u'none', u'zlib@openssh.com'] server compress:[u'none',
u'zlib@openssh.com'] client lang:[u''] server lang:[u''] kex follows?False
ssh: Ciphers agreed: local=aes128-ctr, remote=aes128-ctr
ssh: using kex diffie-hellman-group14-sha1; server key type ssh-rsa;
cipher: local aes128-ctr, remote aes128-ctr; mac: local hmac-sha1, remote
hmac-sha1; compression: local none, remote none
ssh: Switch to new keys ...
ssh: Trying SSH agent key 9516223a1b48a28b1990acb9431bcaac
ssh: userauth is OK
ssh: Authentication (publickey) failed.
ssh: Trying SSH agent key 075fb8fef979f051e824e8a7cfdce59b
ssh: userauth is OK
ssh: Authentication (publickey) failed.
ssh: Trying SSH agent key cd36d7cde74b97d3e2e87c42f57b2305
ssh: userauth is OK
ssh: Authentication (publickey) successful!
ssh: [chan 1] Max packet in: 32768 bytes
ssh: [chan 1] Max packet out: 32768 bytes
ssh: Secsh channel 1 opened.
ssh: [chan 1] Sesch channel 1 request ok
ssh: [chan 1] Opened sftp connection (server version 3)
ssh: [chan 1] stat('Documents')
ssh: [chan 1] stat('Documents')
ssh: [chan 1] normalize('Documents')
Main action: full
================================================================================
duplicity 0.6.24 (May 09, 2014)
Args: /usr/bin/duplicity -v9 full /home/rburgin/Documents
ssh://duplicity@78.143.255.136/Documents
Linux Ricky-PC 3.17.7-300.fc21.x86_64 #1 SMP Wed Dec 17 03:08:44 UTC 2014
x86_64 x86_64
/usr/bin/python 2.7.8 (default, Nov 10 2014, 08:19:18)
[GCC 4.9.2 20141101 (Red Hat 4.9.2-1)]
================================================================================
Using temporary directory /tmp/duplicity-Gbd4V3-tempdir
Registering (mkstemp) temporary file /tmp/duplicity-Gbd4V3-tempdir/mkstemp-
TAALWO-1
Temp has 4171616256 available, backup will use approx 34078720.
ssh: [chan 1] listdir('/home/duplicity/Documents/.')
Local and Remote metadata are synchronized, no sync needed.
ssh: [chan 1] listdir('/home/duplicity/Documents/.')
0 files exist on backend
2 files exist in cache
Extracting backup chains from list of files: []
Last full backup date: none
Collection Status
-----------------
Connecting with backend: SSHParamikoBackend
Archive directory:
/home/rburgin/.cache/duplicity/2ce2771e0b9865a5d162e53ca22a5987

Found 0 secondary backup chains.
No backup chains with active signatures found
No orphaned or incomplete backup sets found.
PASSPHRASE variable not set, asking user.
GnuPG passphrase: ssh: Sending global request "keepalive@lag.net"



And any other IPv4-only host should naturally work.
```
Original tags: ipv6

Story points: 10.0