CBIDXT-130: rebalance.

- fixes to handle StreamEnd and upstream connection closing on dataport.
- udpated local structure that maintains active-vbuckets.
- added RepairVbuckets{} message to differentiate StreamEnd and
  closed-connection.
- when a remote connection gets closed, dataport-server will not close all
  other connections to same client. `closeremote` handling is replaced with
  `closeconn`

Change-Id: I88f70382b80d0fe9d821d1a1d6027ad046e05d32
Reviewed-on: http://review.couchbase.org/40410
Reviewed-by: John Liang <johliang00@gmail.com>
Reviewed-by: Pratap Chakravarthy <prataprc@couchbase.com>
Tested-by: Pratap Chakravarthy <prataprc@couchbase.com>