Add functions EnableMirroringModule and DisableMirroringModule for
turning on an off the mirroring module at the ceph mgr.
This also adds the lower level EnableModule and DisableModule that take
a string parameter naming the module, and are the base for
EnableMirroringModule and DisableMirroringModule.
Signed-off-by: John Mulligan <jmulligan@redhat.com>