Salt module version check

From @Martin-Weiss

". . . add a function to ceph-salt that can detect version differences of modules.. (ceph salt brings new modules so it should also be able to verify the module version on the salt-master and on the salt-clients I hope..)"

Thus, when the ceph-salt-formula RPM is updated and the user forgets to run "saltutil.sync_all", `ceph-salt` would detect a version number mismatch and refuse to continue. Instead, it would instruct the user to run "saltutil.sync_all" and try again.

IMO this would be a great thing to have.

Start by tracing the ceph-salt execution path that runs after a ceph-salt-formula RPM update and identify how Salt modules are currently synchronized. The feature should compare module versions on the salt-master and salt-clients, refuse to continue on a mismatch, and instruct the user to run "saltutil.sync_all" before trying again.

Written by the indexing model from the issue text.