Reload HA configuration when policy is changed.

After policy is changed make sure that HA configuration is reloaded.
This is needed by the cf-serverd as we don't want to restart it all
the time HA configuration is changed.
I was thinking about putting this after KeepPromises(). Right now is doesn't matter as this is only setting HA related things and it is quite independent from the rest of policy. Nevertheless HA status is checked before policy is examined so in future we might have some dependencies which should be resolved before KeepPromises will be called.
Keeping this in locked state also makes sense IMHO. We don't want to face situation when HA configuration will be inconsistent with the rest of policy. This is not so important at the moment (as mentioned above) but might be in future.
Putting in PolicyUpdateIfSafe() seems to be sensible if we are going to have #1927 in 3.6.x.