Revert change to set state of vbucket to "pending" (instead of replica) on new master during takeover (MB-16292)

I spoke with Matt about the change fixing MB-16292 going in to 3.1.4.

Matt's concerned about setting the state on the new master to "pending". The reason is that the pending state blocks until the vbucket state changes to active so for clients like libcouchbase that consult the fast forward map all requests against that node (even other vbuckets) will be blocked until the takeover completes. This should be pretty fast but as we have seen in cases in production takeover can be prolonged and even if the time is seconds that's a long time for a client to be blocked on all requests against a node.

There should be a discussion about what "pending" should return but at least for 3.1.4 the safe option seems to be to revert the fix for MB-16292.