Sync charms.ceph and use helper functions to determine
whether any changes in the source configuration option
are a supported upgrade path.
If an upgrade path is detected then upgrade via apt_install
with the full list of required packages for the radosgw to
force an upgrade.
Change-Id: I48a8b5d14ad6ac11af57ddf0260a4a41744e7e21
Closes-Bug: 1539335
0f3203b18c