race condition in startup of collector service, message dispatched before dispatcher loaded

There's a rare race in the CollectorService startup sequence, such that messages can be dispatched before the dispatcher_manager has been loaded.

The log signature of this race condition is this error is:

2014-09-19 17:55:21.049 20602 TRACE ceilometer.openstack.common.rpc.amqp Traceback (most recent call last):
2014-09-19 17:55:21.049 20602 TRACE ceilometer.openstack.common.rpc.amqp File "/usr/lib/python2.7/site-packages/ceilometer/openstack/common/rpc/amqp.py", line 462, in _process_data
2014-09-19 17:55:21.049 20602 TRACE ceilometer.openstack.common.rpc.amqp **args)
2014-09-19 17:55:21.049 20602 TRACE ceilometer.openstack.common.rpc.amqp File "/usr/lib/python2.7/site-packages/ceilometer/openstack/common/rpc/dispatcher.py", line 172, in dispatch
2014-09-19 17:55:21.049 20602 TRACE ceilometer.openstack.common.rpc.amqp result = getattr(proxyobj, method)(ctxt, **kwargs)
2014-09-19 17:55:21.049 20602 TRACE ceilometer.openstack.common.rpc.amqp File "/usr/lib/python2.7/site-packages/ceilometer/collector.py", line 106, in record_metering_data
2014-09-19 17:55:21.049 20602 TRACE ceilometer.openstack.common.rpc.amqp self.dispatcher_manager.map_method('record_metering_data',
2014-09-19 17:55:21.049 20602 TRACE ceilometer.openstack.common.rpc.amqp AttributeError: 'CollectorService' object has no attribute 'dispatcher_manager'