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>
MB-10057: implemented REST API for incoming xdcr checkpointing

Change-Id: Iacdb11fc021a73bb6e2f5ab92a2f88937fdfcfc0
Reviewed-on: http://review.couchbase.org/34039
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
MB-10057: replaced outgoing xdcr checkpointing implementation

Change-Id: Ia540f770c2daebff386a3bcc6acc782f4a83eb07
Reviewed-on: http://review.couchbase.org/34040
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>