detect_stale_master option added in mysql_mon

detect_stale_master option added in mysql_mon.
A previous detected Master may be used again (so it’s called Stale
Master) if all the slaves have a stopped replication setup (i.e both IO
and SQL threads are not woking in slaves)
The SERVER_STALE_STATUS is set and reported in server status, example:
“Master, Stale Status, Running”

After MaxScale monitor restart no master will be available if the
replication is still not running or not configured.
The option is not enable by default.