Add python3-packaging

Newer release(s) of Ceph require the python3-packaging deb package, and
it's not being declared as a dependency, so the charm needs to handle
this.

This change was merged in master in commit
a465929ece although it can't be
cherry-picked since the change is part of a larger patch that shouldn't
be backported.

Change-Id: I8a92ee7604d3107fad7680dfd1b868f337346d5a
Closes-Bug: #2064717

hooks/ceph_hooks.py

@@ -322,7 +322,11 @@ def install_udev_rules():
 def install():
     add_source(config('source'), config('key'))
     apt_update(fatal=True)
-    apt_install(packages=ceph.determine_packages(), fatal=True)
+    packages = ceph.determine_packages()
+    # TODO(chrome0): temp. fix for bug #2064717; remove once this has been
+    # fixed
+    packages.append('python3-packaging')
+    apt_install(packages=packages, fatal=True)
     if config('autotune'):
         log('The autotune config is deprecated and planned '
             'for removal in the next release.', level=WARNING)