CC-3520: Change default password of monit

-currently I allow it to be fixed, but I don't actually change it
from default of airtime:guest

install_minimal/upgrades/airtime-2.1.0/etc/airtime.conf.210

@@ -22,6 +22,10 @@ base_port = 80
 ;cache scheduled media files.
 cache_ahead_hours = 1
 
+[monit]
+user = guest
+password = airtime
+
 [soundcloud]
 connection_retries = 3
 time_between_retries = 60