mon,auth: fix proposal of rotating keys

mon,auth: fix proposal of rotating keys

Instead of updating the live CephxKeyServer's rotating_keys and also
including them in a paxos proposal, propose new keys only in the proposal,
and only make them live once they are committed.  This keeps mons fully in
sync and avoids any inconsistency between the live behavior and committed
state (e.g., stale or divergent keys being applied and passed out to
daemons).

Signed-off-by: Sage Weil <sage@newdream.net>