MB-10641 Open a new checkpoint on replica vbucket if required.

There is a case where a given replica is promoted to the new
master when it already receives CHECKPOINT_END message, but not
CHECKPOINT_START message yet from the old master that was just
crashed. In this case, we should open a new checkpoint in the
new master.

Change-Id: Ic525acad7eb9285eb0c040fd7455e7e64ce2893d
Reviewed-on: http://review.couchbase.org/34925
Reviewed-by: Michael Wiederhold <mike@couchbase.com>
Reviewed-by: Chiyoung Seo <chiyoung@couchbase.com>
Tested-by: Chiyoung Seo <chiyoung@couchbase.com>