Crashes on initial backup with python NotImplementedError (lp:#1641338)

[Original report](https://bugs.launchpad.net/bugs/1641338) created by **Will Pimblett (wjdp)**
```
Command

`duplicity --exclude-filelist=~/.backup_exclude -v8 $HOME
amazondrive:///backup/frank-family`

Returns the following

```
Using archive dir:
/home/will/.cache/duplicity/bc43d4b7e72909b8f8e51e0a92de7c81
Using backup name: bc43d4b7e72909b8f8e51e0a92de7c81
Import of duplicity.backends.localbackend Succeeded
Import of duplicity.backends.cfbackend Succeeded
Import of duplicity.backends.dpbxbackend Succeeded
Import of duplicity.backends.gdocsbackend Succeeded
Import of duplicity.backends.tahoebackend Succeeded
Import of duplicity.backends.u1backend Succeeded
Import of duplicity.backends.rsyncbackend Succeeded
Import of duplicity.backends.swiftbackend Succeeded
Import of duplicity.backends.hsibackend Succeeded
Import of duplicity.backends.megabackend Succeeded
Import of duplicity.backends.botobackend Succeeded
Import of duplicity.backends.ftpsbackend Succeeded
Import of duplicity.backends.imapbackend Succeeded
Import of duplicity.backends.webdavbackend Succeeded
Import of duplicity.backends.sshbackend Succeeded
Import of duplicity.backends.amazondrivebackend Succeeded
Import of duplicity.backends.ftpbackend Succeeded
Could not load OAuth2 token. Trying to create a new one. (original error:
[Errno 2] No such file or directory:
'/home/will/.duplicity_amazondrive_oauthtoken.json')

In order to allow duplicity to access AmazonDrive, please open the
following URL in a browser and copy the URL of the page you see after
authorization here:

~~~

Reading filelist /home/will/.backup_exclude
Sorting filelist /home/will/.backup_exclude
Main action: inc
================================================================================
duplicity 0.6.23 (January 24, 2014)
Args: /usr/bin/duplicity --exclude-filelist=~/.backup_exclude -v8
/home/family amazondrive:///backup/frank-family
Linux frank 3.13.0-93-generic #140-Ubuntu SMP Mon Jul 18 21:20:08 UTC 2016
i686 i686
/usr/bin/python 2.7.6 (default, Jun 22 2015, 18:00:18)
[GCC 4.8.2]
================================================================================
Using temporary directory /tmp/duplicity-4WhJ6m-tempdir
Temp has 998864809984 available, backup will use approx 34078720.
Local and Remote metadata are synchronized, no sync needed.
Last full backup date: none
Collection Status
-----------------
Connecting with backend: AmazonDriveBackend
Archive directory:
/home/will/.cache/duplicity/bc43d4b7e72909b8f8e51e0a92de7c81

Found 0 secondary backup chains.
No backup chains with active signatures found
No orphaned or incomplete backup sets found.
No signatures found, switching to full backup.
Using temporary directory
/home/will/.cache/duplicity/bc43d4b7e72909b8f8e51e0a92de7c81/duplicity-
AUO4M3-tempdir
Using temporary directory
/home/will/.cache/duplicity/bc43d4b7e72909b8f8e51e0a92de7c81/duplicity-060O9H-tempdir
AsyncScheduler: instantiating at concurrency 0
A .
Error accessing possibly locked file /home/family/.bash_history
Error accessing possibly locked file /home/family/.btsync
Error accessing possibly locked file /home/family/.cache
Error accessing possibly locked file /home/family/.config
A .excluded_from_backup
A .hplip
A .hplip/hplip.conf
Error accessing possibly locked file /home/family/.lesshst
A .share
A .share/hf
A .share/hf/Documents
A .share/hf/Music
A .share/hf/Photos
A .share/media
A .share/media/.DS_Store
A .share/media/Films
A .share/media/Music
A .share/media/Photos
A .share/media/Recordings
A .share/media/TV Shows
A .share/util
A .share/util/.DS_Store
A .share/util/AbsoluteUninstaller.exe
A .share/util/ChromeStandaloneSetup.exe
AsyncScheduler: running task synchronously (asynchronicity disabled)
Traceback (most recent call last):
  File "/usr/bin/duplicity", line 1494, in <module>
    with_tempdir(main)
  File "/usr/bin/duplicity", line 1488, in with_tempdir
    fn()
  File "/usr/bin/duplicity", line 1337, in main
    do_backup(action)
  File "/usr/bin/duplicity", line 1463, in do_backup
    full_backup(col_stats)
  File "/usr/bin/duplicity", line 542, in full_backup
    globals.backend)
  File "/usr/bin/duplicity", line 424, in write_multivol
    (tdp, dest_filename, vol_num)))
  File "/usr/lib/python2.7/dist-packages/duplicity/asyncscheduler.py", line
145, in schedule_task
    return self.__run_synchronously(fn, params)
  File "/usr/lib/python2.7/dist-packages/duplicity/asyncscheduler.py", line
171, in __run_synchronously
    ret = fn(*params)
  File "/usr/bin/duplicity", line 423, in <lambda>
    async_waiters.append(io_scheduler.schedule_task(lambda tdp,
dest_filename, vol_num: put(tdp, dest_filename, vol_num),
  File "/usr/bin/duplicity", line 314, in put
    backend.put(tdp, dest_filename)
  File "/usr/lib/python2.7/dist-packages/duplicity/backend.py", line 397,
in put
    raise NotImplementedError()
NotImplementedError

```
```

Story points: 6.0