protobuf/* (updated mutation protobuf definition)

- Renamed VbucketMutation message to KeyVersions message.
- Renamed fields names for VbConnectionMap message.

Change-Id: I16ba71644efbe4335afe0768a6b597fa16c5e65f
Reviewed-on: http://review.couchbase.org/35602
Reviewed-by: John Liang <johliang00@gmail.com>
Reviewed-by: Deepkaran Salooja <deepkaran.couchbase@gmail.com>
Reviewed-by: Pratap Chakravarthy <prataprc@couchbase.com>
Tested-by: Pratap Chakravarthy <prataprc@couchbase.com>