Revert "Use Juju 2.9.12"

This reverts commit f5051cb9

.

Reason for revert: 

Juju 2.9.12 has bugs that require us to stick with original until they are fixed.

Change-Id: I4f5b7af7278b67c39c9e236fa67e051eccf295e7
Signed-off-by: beierlm <mark.beierl@canonical.com>