Move declaration of int_br_device_count earlier

_report_state is being called by setup_rpc so int_br_device_count needs
to be initialized earlier. To avoid
AttributeError: object has no attribute 'int_br_device_count'

This wasn't caught by unit tests for 3 separate reason
o The reference to self.int_br_device_count is wrapped in
  except Exception: log / pass
- This reference has been moved outside of the try/except

o Unit tests set report_interval to 0 so the heartbeat wasn't called
  during unit tests.
- now removed

o The function passed into FixedIntervalLoopingCall isn't started
  anyways so wasn't calling self._report_state
- replaced FixedIntervalLoopingCall with a mock that calls the
  function once.

Fixes bug #1221054

Change-Id: I572af4ee017c1f7f016c8f9981ca54d1301442d1
Merge "Move declaration of int_br_device_count earlier"