MB-7935: Disabling setting vbuckets to dead state

- During warmup, ns_server blocks connections to vbuckets,
so ep-engine doesn't need to set the vbucket states to dead.
- master branch (for next release)

Change-Id: I095adfe0253c28212d8b46b6193c47771d5bee78
Reviewed-on: http://review.couchbase.org/26763
Reviewed-by: Chiyoung Seo <chiyoung.seo@gmail.com>
Tested-by: Chiyoung Seo <chiyoung.seo@gmail.com>