Support external programs can take the initiative to call API ceilometer allows ceilometer to collect external application concerns meter

Ceilometer can now only be based on the acquisition cycle of pipeline.yaml, the timing of the acquisition of a variety of information. Call API ceilometer can only query to these timing acquisition of information, can not achieve the external application of the initiative to request ceilometer-api to collect information
The current design idea is the following:
1.Add a new API ceilometer, the external program calls this API will send information to the queue, ceilometer-compute-agent will be based on the information inside the queue, call the relevant poller to take the initiative to obtain information
2.In the original timing acquisition mechanism is still retained, the development function, will not change any of the original code, only to the original function is extended, the user can take is using the original acquisition mechanism, or the use of active call API to trigger active acquisition