mon/Paxos: fix off-by-one in last_ vs first_committed check

peon last_committed + 1 == leader first_committed is okay.  Note that the
other check (where I clean up whitespace) gets this correct.

Fixes: #9301 (partly)
Signed-off-by: Sage Weil <sage@redhat.com>
mon: re-bootstrap if we get probed by a mon that is way ahead

During bootstrap we verify that our paxos commits overlap with the other
mons we will form a quorum with.  If they do not, we do a sync.

However, it is possible we pass those checks, then fail to join a quorum
before the quorum moves ahead in time such that we no longer overlap.
Currently nothing kicks up back into a probing state to discover we need
to sync... we will just keep trying to call or join an election instead.

Fix this by jumping back to bootstrap if we get a probe that is ahead of
us.  Only do this from non probe or sync states as these will be common;
it is only the active and electing states that matter (and probably just
electing!).

Fixes: #9301
Backport: giant, firefly
Signed-off-by: Sage Weil <sage@redhat.com>
Merge remote-tracking branch 'gh/wip-9301'

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