Changing Juju version in Docker

The juju that is integrated in the LCM container,
contains a pinned version and needs to be updated
for new functionality.

Change-Id: Ia5b86260689ac8f6e32f080ccd0bbbce79b9afac
Signed-off-by: Dominik Fleischmann <dominik.fleischmann@canonical.com>
(cherry picked from commit 40e73bfe)