MB-8439 add decrDiskQueueSize method instead of undercount assert

DiskQueueSuze is no longer a critical variable for flusher and
checkpoint manager's decision making logics. It is simply a stat
indicating current pending disk write.

At any given point if this stat is undercounted we should just log
a warning and continue instead of assert. Otherwise, the assert
could cause a serious data loss for the crashed node.

Change-Id: I97d7b0ed6e6348578c3f35c373de779a21f469ed
Reviewed-on: http://review.couchbase.org/26897
Reviewed-by: Chiyoung Seo <chiyoung.seo@gmail.com>
Tested-by: Chiyoung Seo <chiyoung.seo@gmail.com>
CBD-963:  empty commit to create 2.1.1 branch

Change-Id: I26b122a697dc93e20347b79992c39f6233c162ca
Reviewed-on: http://review.couchbase.org/27016
Reviewed-by: Philip Labee <philip@couchbase.com>
Tested-by: Philip Labee <philip@couchbase.com>
MB-8244 add EXECUTOR_WAITING & EXECUTOR_SLEEPING

This new states will be useful for indicating which
exucutor thread (readers/writers) is waiting. This
will be available as part of readers/writers stat.

Change-Id: Id6179855ca2d430bc7d1356b40e231a1506be2b5
Reviewed-on: http://review.couchbase.org/27038
Reviewed-by: Michael Wiederhold <mike@couchbase.com>
Tested-by: Jin Lim <jin@couchbase.com>
MB-8244 add currentTask to track currently executing task

Change-Id: I5d65ab1e2a959232d0a43abd410290344e343a6f
Reviewed-on: http://review.couchbase.org/27060
Reviewed-by: Jin Lim <jin@couchbase.com>
Tested-by: Jin Lim <jin@couchbase.com>
MB-8464: Fix crash in test_checkpoint_persistence

- test_checkpoint_persistence seen to be failing
sometimes only in Linux due to a race condition
- adjusting the checkpoint_flush_timeout before
notifying_IO_completion during notify_checkpoint_
persisted seems to have stopped this error from
occuring.

Change-Id: I6804cb9dc566e9f0d2ed831c694feda19491762a
Reviewed-on: http://review.couchbase.org/27155
Reviewed-by: Michael Wiederhold <mike@couchbase.com>
Tested-by: Michael Wiederhold <mike@couchbase.com>
MB-8467 Reset notifySent flag upon vbucket filter changes.

When the TAP producer receives the vbucket filter change
request from the cluster manager, it should set notifySent
flag to false, so that the TAP producer can send the TAP
OPAQUE response to the cluster manager immediately in order to
notify that the filter change request was successfully applied.

Otherwise, there can be 5 seconds unnecessary delay in sending
the reponse to the cluster manager.

Change-Id: Ie9e7720d6d2ff8a71040a95963b2065a4a58686e
Reviewed-on: http://review.couchbase.org/27156
Reviewed-by: Chiyoung Seo <chiyoung.seo@gmail.com>
Tested-by: Chiyoung Seo <chiyoung.seo@gmail.com>
Merge remote-tracking branch 'gerrit/2.1.1' into master

Change-Id: I9c84555c8983554864656995db62c6b9fe2149d8