MB-12063 Don't delete expired items during warmup.

When a node is added back to the cluster, its vbucket states
can be different from its previous states (e.g., active -> replica).
Therefore, we should not remove expired items from active vbuckets
during warmup because the states of those vbuckets can be changed
after the warmup.

Change-Id: Ifec4fda80e424a8afa74bae66e17de77b2e0c36b
Reviewed-on: http://review.couchbase.org/41219
Reviewed-by: Chiyoung Seo <chiyoung@couchbase.com>
Tested-by: Chiyoung Seo <chiyoung@couchbase.com>
MB-12137: Don't update the current snapshot during persistence

If we update the current snapshot only when we persist items to
disk then we may miss out on updates to the current snapshot
when there are vbucket state changes.

Change-Id: Iea3139afb669bdf32e6b4d98e8b3515cafe578dc
Reviewed-on: http://review.couchbase.org/41289
Reviewed-by: Chiyoung Seo <chiyoung@couchbase.com>
Tested-by: Michael Wiederhold <mike@couchbase.com>
Merge remote-tracking branch 'gerrit/3.0' into 3.0.1

Change-Id: I195452c3d0684dff5ff673efd00a18b9d70da3cf