MB-10057: implemented vbuuid creation

The trick we use is to update vbucket database during mccouch
notification. At this time we know that ep-engine does not touch
.couch file.

Notable implementation detail is that we have to manually spawn
duplicate couchdb process for actual update. That's because normal
couchdb instance we have for normal vbuckets refuse any updates (which
is a feature).

Change-Id: I1e245ef0462cfc45d282fe66c78f9a80f97e582c
Reviewed-on: http://review.couchbase.org/34038
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Merge commit 'cdf2f783961b024242c9b715ea6ca20106891687' into master

* commit 'cdf2f783961b024242c9b715ea6ca20106891687':
  MB-10057: implemented vbuuid creation

This is just formal merge. No actual code is merged because 2.5.1's
implementation is not right for 3.0

Change-Id: I45178b8aa0cbd8454b71660290ab548bc368935b
MB-10057: implemented basic get_local_vbuuid/2 for 3.0

Not that it's not kind of checkpointing we ultimately want in 3.0. But
in order to merge 2.5.1 stuff it's best to start simple.

This implementation is taking vbucket uuid from failover id using stat
request. And notably, unlike 2.5.1 it will not tolerate crashes due to
3.0's failover id change on unclean shutdown.

Change-Id: I4e63041bcd84c70a1732d20109e69900e2814a2e
Reviewed-on: http://review.couchbase.org/34455
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>