mgr: forward RADOS client instances for potential blacklist

mgr: forward RADOS client instances for potential blacklist

The mgr creates a per-module RADOS client connection for modules which
interact with RADOS (e.g. the volumes module). These clients should also
be blacklisted when the active mgr is failed; we don't want the former
active mgr to continue interacting with RADOS when the new one takes
over. This is particularly impactful for avoiding extraneous
"unresponsive client" warnings from the MDS when the mgr switches
(especially in testing). The MDS will pickup the new OSD blacklists
which include's the old mgr's libcephfs instance and blacklist/evict
that session quietly.

Signed-off-by: Patrick Donnelly <pdonnell@redhat.com>