mon: Monitor: s/_mon_status()/get_mon_status()/

mon: Monitor: s/_mon_status()/get_mon_status()/

'Monitor::_mon_status()' provides status specific to the monitor being
poked.  This is information that does not necessarily relate with
cluster status, and can even be obtained when there's no quorum (via the
admin socket).

We change the function name to make the distinction between mon-specific
status and cluster-status, which is obtained via a different function.

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