CBQE:0 XDCR checkpointing - Remove vb_high_seqno check on commitopaque, it needn't match and kill memc instead of erlang in crash tests

Change-Id: I695e2d192c331ec9f7bf9aea2edec3ab8db17eec
Reviewed-on: http://review.couchbase.org/38858
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>
Tested-by: Aruna Piravi <aruna@couchbase.com>