MB-11176 Detect vbucket resets by checking start_seqno > end_seqno

During special scenarios like upgrade from Couchbase 2.0 to Couchbase 3.0,
UPR server may reset vbuckets multiple times and hence end_seqno might
become lower than last indexed sequence number. The end_seqno is obtained
from vbucket-seqno stats and it gets resetted when a vbucket reset happens.
In such an event, view engine should optimistically check if a rollback is
required and should perform index rollback.

Change-Id: I6a702adb05f2207e2adcde20e7c418d00393c4cc
Reviewed-on: http://review.couchbase.org/38876
Reviewed-by: Sarath Lakshman <sarath@couchbase.com>
Reviewed-by: Nimish Gupta <nimish@couchbase.com>
Tested-by: Sarath Lakshman <sarath@couchbase.com>