MB-29287: Merge commit 'couchbase/watson_ep~1' into couchbase/5.1.0

This commit is already present in the 5.1.0 branch (this is
a backport of that fix). Mark it as merged to make subsequent
merge of couchbase/watson_ep easier.

Merged with

    git merge -s ours --no-ff --log couchbase/watson_ep~1

* commit 'couchbase/watson_ep~1':
  MB-29381: Allow DCP rollback on vbuckets in pending state

Change-Id: Ib4d08ae292da489bd49cc084bccda4f80c9c90e0

Author: trondn