osd,mds,mgr: do not dereference null rotating_keys

osd,mds,mgr: do not dereference null rotating_keys

Immediately after we bind to a port, but before we have set up our
auth infrastructure, we may get incoming connections.  Deny them.  Since
we are not yet advertising ourselves these are peers trying to connect
to old instances of daemons, not us.

This triggers now because of bf4938567943c80345966f9c5a3bdc75a913175b.
Previously, the peer would see we were a different addr and drop the
connection.  Now, it continues.

Fixes: http://tracker.ceph.com/issues/20667
Signed-off-by: Sage Weil <sage@redhat.com>