Install Paramiko and GObject2

Without the `python-paramiko` or `python-gobject-2` packages installed,
the installation of th Gio and SSH Duplicity backends will fail:

  Import of duplicity.backends.giobackend Failed: No module named gio
  Import of duplicity.backends.sshbackend Failed: No module named paramiko

Install these two packages.

For further details, see
http://www.rfc3092.net/2013/09/missing-modules-for-paramiko-and-gio-in-duplicity-foo/