backport juju plugin from 3.2-alpha

Description: Backport the juju plugin from 3.2-alpha version

Author: Louis Bouchard <louis.bouchard@canonical.com>
Ubuntu-Bug: http://bugs.launchpad.net/bugs/1363155

Signed-off-by: Louis Bouchard <louis.bouchard@canonical.com>
merge patched-ubuntu/utopic-juju into ubuntu/utopic-juju
change version to 3.1-1ubuntu4
debian/patches/0010-backport-juju-plugin-from-3.2-alpha.patch
- Backport the juju plugin from 3.2-alpha version
(LP: #1363155)