ceph.in: only shut down rados on clean exit

ceph.in: only shut down rados on clean exit

If we exit due to a timeout, then calling rados shutdown can lead to all
sorts of problems, because we may still have another thread that is
trying to call rados_connect and/or do some work, and rados_connect
and rados_shutdown don't (and can't!) really behave well when racing
against each other.

Note that shutdown here isn't that important--the process is about to
exit anyway.  It's only useful to exercise the shutdown code path more
often.

Fixes: https://tracker.ceph.com/issues/44526
Signed-off-by: Sage Weil <sage@redhat.com>