mon: use vector<MonCommand> throughput for commands

mon: use vector<MonCommand> throughput for commands

The old code was pretty messy. This is standardizes on std::vector
throughout.  We also drop the win_election command args because
when we win an election we always set the leader commands to our
commands, and we can do that inside win_command() without passing
them in from here.

Signed-off-by: Sage Weil <sage@redhat.com>
(cherry picked from commit 349b3c9bef12728c336cf584ea5c70b8184b66e9)