MB-29381: Merge branch 'couchbase/watson_ep' into 'couchbase/spock'

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

Note: This merge is deliberately side-stepping the couchbase/5.1.0
branch and going directly from watson to spock

Change-Id: If7be26fd9cec27616ceca6998ba9669a0c1b7d52

Author: jimwwalker