MB-24066/MB-22178: Set opencheckpointid to 1 after rollback

MB-24066/MB-22178: Set opencheckpointid to 1 after rollback

An opencheckpoint of 0 has the special meaning of being in a backfill
phase.

Therefore after performing a rollback we must ensure the
opencheckpointid is reset to 1.  This is the value used when the
vbucket is originally intialised.

Change-Id: I6b97faa7b502406961a4b48ad7affdbf6bc30512
Reviewed-on: http://review.couchbase.org/77837
Well-Formed: Build Bot <build@couchbase.com>
Reviewed-by: Dave Rigby <daver@couchbase.com>
Tested-by: Build Bot <build@couchbase.com>