mon: tell MonmapMonitor first about winning an election

It is important in the bootstrap case that the very first paxos round
also codify the contents of the monmap itself in order to avoid any manner
of confusing scenarios where subsequent elections are called and people
try to recover and modify paxos without agreeing on who the quorum
participants are.

Signed-off-by: Sage Weil <sage@inktank.com>