CBIDXT-121 Initial Implementation of Scan Coordinator

Also changes in CbqBridge to make queries work

Patchset2:
Better handling for stop channel to abort scans

Change-Id: Idd9f8667d1eeaf6a667cf0cb18b86b99e60c669f
Reviewed-on: http://review.couchbase.org/40262
Reviewed-by: Deepkaran Salooja <deepkaran.couchbase@gmail.com>
Tested-by: Deepkaran Salooja <deepkaran.couchbase@gmail.com>