Fixes bug #1078773
The worker stats thread now checks to see if haproxy is running
before attempting to get stats from it. If it isn't running, a
ServiceUnavailable exception is thrown and it goes back to sleep
until the next polling interval.
Also rename config_manager and stats_manager functions to
config_thread and stats_thread to make their purpose a bit clearer.
Change-Id: I01e2c86bcac81a00027d4a7201feb922c6e72f3b
cc7f07dc3b