PyDrive Backend Fails: RelativeURIError (lp:#1540161)

[Original report](https://bugs.launchpad.net/bugs/1540161) created by **JP (0j-p)**
```
Updated duplicity 2016-01-29 in Changelog.GNU, ran my backup script for
pydrive and hit this error:

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.copycombackend Succeeded
Import of duplicity.backends.dpbxbackend Succeeded
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.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 Failed: No module named kerberos
Using temporary directory /tmp/duplicity-TdL142-tempdir
Traceback (most recent call last):
  File "/usr/local/bin/duplicity", line 1537, in <module>
    with_tempdir(main)
  File "/usr/local/bin/duplicity", line 1531, in with_tempdir
    fn()
  File "/usr/local/bin/duplicity", line 1369, in main
    action = commandline.ProcessCommandLine(sys.argv[1:])
  File "/usr/local/lib/python2.7/dist-packages/duplicity/commandline.py",
line 1116, in ProcessCommandLine
    backup, local_pathname = set_backend(args[0], args[1])
  File "/usr/local/lib/python2.7/dist-packages/duplicity/commandline.py",
line 1005, 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/pydrivebackend.py", line 58, in __init__
    file_list = self.drive.ListFile({'q': "'Root' in parents and
trashed=false"}).GetList()
  File "/usr/local/lib/python2.7/dist-packages/pydrive/apiattr.py", line
154, in GetList
    for x in self:
  File "/usr/local/lib/python2.7/dist-packages/pydrive/apiattr.py", line
138, in next
    result = self._GetList()
  File "/usr/local/lib/python2.7/dist-packages/pydrive/auth.py", line 54,
in _decorated
    return decoratee(self, *args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/pydrive/files.py", line 56,
in _GetList
    self.metadata = self.auth.service.files().list(**dict(self)).execute()
  File "/usr/local/lib/python2.7/dist-packages/oauth2client/util.py", line
140, in positional_wrapper
    return wrapped(*args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/googleapiclient/http.py",
line 722, in execute
    body=self.body, headers=self.headers)
  File "/usr/local/lib/python2.7/dist-packages/oauth2client/client.py",
line 596, in new_request
    redirections, connection_type)
  File "/usr/lib/python2.7/dist-packages/httplib2/__init__.py", line 1440,
in request
    (scheme, authority, request_uri, defrag_uri) = urlnorm(uri)
  File "/usr/lib/python2.7/dist-packages/httplib2/__init__.py", line 217,
in urlnorm
    raise RelativeURIError("Only absolute URIs are allowed. uri = %s" %
uri)
RelativeURIError: Only absolute URIs are allowed. uri =
https:/drive/v2/files?q=%27Root%27+in+parents+and+trashed%3Dfalse&alt=json&maxResults=1000
```

Story points: 6.0