MB-7022 Remove the empty flush queues for non-existent vbuckets
MB-7022 Remove the empty flush queues for non-existent vbuckets

We maintain a separate flush queue per vbucket, but should
remove the empty flush queue if its vbucket doesn't exist
anymore on a given node.

Change-Id: Ie43ccf06d5b8c8c26efddbbabef65e1acbff8e2d
Reviewed-on: http://review.couchbase.org/21976
Tested-by: buildbot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: Jin Lim <c45cd80a556f432a3607171a6818cd5a074b5cd4@couchbase.com>
Tested-by: Jin Lim <c45cd80a556f432a3607171a6818cd5a074b5cd4@couchbase.com>

hisundar/ep-engine,abhinavdangeti/ep-engine,owendCB/ep-engine,daverigby/ep-engine,owendCB/ep-engine,daverigby/kv_engine,abhinavdangeti/ep-engine,daverigby/kv_engine,abhinavdangeti/ep-engine,teligent-ru/ep-engine,couchbase/ep-engine,hisundar/ep-engine,daverigby/ep-engine,owendCB/ep-engine,couchbase/ep-engine,sriganes/ep-engine,teligent-ru/ep-engine,daverigby/kv_engine,jimwwalker/ep-engine,sriganes/ep-engine,daverigby/ep-engine,membase/ep-engine,jimwwalker/ep-engine,daverigby/ep-engine,sriganes/ep-engine,hisundar/ep-engine,membase/ep-engine,abhinavdangeti/ep-engine,hisundar/ep-engine,teligent-ru/ep-engine,couchbase/ep-engine,membase/ep-engine,jimwwalker/ep-engine,membase/ep-engine,owendCB/ep-engine,abhinavdangeti/ep-engine,couchbase/ep-engine,sriganes/ep-engine,jimwwalker/ep-engine,daverigby/kv_engine,teligent-ru/ep-engine