TS-2931: plugin metrics fail after a crash

If a plugin uses TSStatFindName followed by TSStatCreate, TSStatFindName
can return 0 for all the metric IDs after a traffic_server crash.

This will happen every time with the following conditions:
  1. traffic_manager has pulled the stat records from traffic_server
  2. traffic_server crashes

When traffic_server comes back up, it pulls the records from
traffic_manager. traffic_manager sends the records including the
rsb_id field. However, RecForceInsert() does not copy the rsb_id
field from the message to the actual record. Subsequent stat lookups
succeed because the stat is registered, but always receive a rsb_id
of 0.

The fix is to ensure that we copy the rsb_id field so that stat
lookups succeed.