Investigate the concurrent execution of DynamicArchive dumping

DynamicArchive dumping can occur in two ways:
1. during VM shutdown in before_exit()
2. via jcmd VM.cds dynamic_dump

It is possible that both of the above could happen concurrently.

Investigate if the DynamicArchive dump logic is capable of handling concurrent execution (we know the preparatory phase of dumping can not). Otherwise, a lock is needed to ensure the dumping operation is performed one at a time.