Fixed Arbiter.reload_from_config (httpd and statsd stopped)

circushttpd and circusd-stats watchers were stopped for no reason.
reload_from_config does not allow [arbiter] changes, so sockets
and watchers created on [arbiter]'s behalf should be ignored when
looking for changes.
Merge pull request #559 from suligap/fix-reload-arbiter-watchers

Fixed Arbiter.reload_from_config (httpd and statsd stopped)