Fix managing runalerts script when HA is enabled.

Make sure that once HA is enabled and hub is NOT working as the active one
runalerts script wont be run. This will eliminate possibility of
having duplicate alert emails from both active and passive hubs.
Add ha_enabled file needed by MP.

In MP first test to figure out if HA is switched on or not is checking
of existence of 'ha_enabled' file. Once HA is enabled file will be created
in directory accessible by httpd to indicate that current hub is working
in HA mode.