mon: PaxosService: remove lingering uses of paxos getters and wait methods

We should use the PaxosServices getters, setters, and wait methods when and
wherever possible.  These must have fallen through the cracks during the
merge.

Signed-off-by: Joao Eduardo Luis <joao.luis@inktank.com>
mon: Monitor: fix signed/unsigned comparison

Signed-off-by: Joao Eduardo Luis <joao.luis@inktank.com>