XD-1408 ensure singleton ContainerMetadata
XD-1396 Fix ContainerRegistrar event handler

The ContainerRegistrar should only process the ContextRefreshedEvent from
the ContainerServerApplication's context refresh event. When an external
management server used, then its context refresh also triggers the
ContainerStartedEvent.
 - Fix ContainerRegistrar's event handler to process the event's source
applicaton context ID equals to that of containerID from ContainerMetadata.