Redmine #6161: Core support for HA checking

As HA is enterprise only feature in core there are some stubs added
that will allow agent to check HA status.
Redmine #6161: Removing HA related log message so in core.

Right now core users wont be flooded by enterprise related message.
Merge pull request #1807 from pasinskim/ha

Redmine #6161: Core support for HA checking