ocfs2/dlm: Add message DLM_QUERY_REGION

Adds new dlm message DLM_QUERY_REGION that sends the names of all active
heartbeat regions. This message is only sent in the global heartbeat
mode. If the regions in the joining node do not fully match the ones in
the active nodes, the join domain request is rejected.

Signed-off-by: Sunil Mushran <sunil.mushran@oracle.com>