Unable to upload data in existing bucket (lp:#1744061)

[Original report](https://bugs.launchpad.net/bugs/1744061) created by **Mislav (mislavorsolic)**
```
Duplicity version: 0.7.16
Python version: 2.7.13
OS Distro and version: Debian 9
Type of target filesystem: Linux, Windows, other.: AWS S3
Log output from -v9 option - Include the command line, the first 200 lines
of the log, and the last 200 lines of the log.

Using archive dir: /root/.cache/duplicity/5a698764f55901efaa11eacfb96afe00
Using backup name: 5a698764f55901efaa11eacfb96afe00
GPG binary is gpg, version 2.1.18
Import of duplicity.backends.acdclibackend Succeeded
Import of duplicity.backends.azurebackend Succeeded
Import of duplicity.backends.b2backend Succeeded
Import of duplicity.backends.botobackend Succeeded
Import of duplicity.backends.cfbackend Succeeded
Import of duplicity.backends.dpbxbackend Failed: No module named dropbox
Import of duplicity.backends.gdocsbackend Succeeded
Import of duplicity.backends.giobackend Succeeded
Import of duplicity.backends.hsibackend Succeeded
Import of duplicity.backends.hubicbackend Succeeded
Import of duplicity.backends.imapbackend Succeeded
Import of duplicity.backends.lftpbackend Succeeded
Import of duplicity.backends.localbackend Succeeded
Import of duplicity.backends.mediafirebackend Succeeded
Import of duplicity.backends.megabackend Succeeded
Import of duplicity.backends.multibackend Succeeded
Import of duplicity.backends.ncftpbackend Succeeded
Import of duplicity.backends.onedrivebackend Succeeded
Import of duplicity.backends.par2backend Succeeded
Import of duplicity.backends.pydrivebackend Succeeded
Import of duplicity.backends.rsyncbackend Succeeded
Import of duplicity.backends.ssh_paramiko_backend Succeeded
Import of duplicity.backends.ssh_pexpect_backend Succeeded
Import of duplicity.backends.swiftbackend Succeeded
Import of duplicity.backends.sxbackend Succeeded
Import of duplicity.backends.tahoebackend Succeeded
Import of duplicity.backends.webdavbackend Succeeded
Using temporary directory /tmp/duplicity-63GCQx-tempdir
Traceback (innermost last):
  File "/usr/local/bin/duplicity", line 1559, in <module>
    with_tempdir(main)
  File "/usr/local/bin/duplicity", line 1545, in with_tempdir
    fn()
  File "/usr/local/bin/duplicity", line 1381, in main
    action = commandline.ProcessCommandLine(sys.argv[1:])
  File "/usr/local/lib/python2.7/dist-packages/duplicity/commandline.py",
line 1140, in ProcessCommandLine
    backup, local_pathname = set_backend(args[0], args[1])
  File "/usr/local/lib/python2.7/dist-packages/duplicity/commandline.py",
line 1015, in set_backend
    globals.backend = backend.get_backend(bend)
  File "/usr/local/lib/python2.7/dist-packages/duplicity/backend.py", line
223, in get_backend
    obj = get_backend_object(url_string)
  File "/usr/local/lib/python2.7/dist-packages/duplicity/backend.py", line
209, in get_backend_object
    return factory(pu)
  File "/usr/local/lib/python2.7/dist-
packages/duplicity/backends/_boto_single.py", line 166, in __init__
    self.resetConnection()
  File "/usr/local/lib/python2.7/dist-
packages/duplicity/backends/_boto_single.py", line 191, in resetConnection
    location=self.my_location)
  File "/usr/lib/python2.7/dist-packages/boto/s3/connection.py", line 620,
in create_bucket
    response.status, response.reason, body)
 S3CreateError: S3CreateError: 409 Conflict
<?xml version="1.0" encoding="UTF-8"?>
<Error><Code>BucketAlreadyOwnedByYou</Code><Message>Your previous request
to create the named bucket succeeded and you already own
it.</Message><BucketName>test-backup-
storage</BucketName><RequestId>6B34D6B947EB3E1C</RequestId><HostId>0W9aKSim3k6b19SJCOObYZVDQ51RjzOH5ElIDV64kw3dGm/jvuQ6R8NVbPFyh4agSu6VL3lsmP8=</HostId></Error>


Why is duplicity trying to create bucket? It already exists. It's located
in AWS S3 - EU (Frankurt). My line is:
duplicity --s3-european-buckets --s3-use-new-style /PATH/TO/UPLOAD/
s3+http://MY-BUCKET-NAME -v9

Am I doing something wrong?
```

Story points: 6.0