CBIDXT-218: bug fix.

Gocouchbase : connection pool overflow.

- getBucket() method is removed from Projector{} and Feed{} instance.
- Projector will immediately close the bucket instance once bucket
  information is obtained.
- Feed will call feeder:CloseFeed() for Shutdown() and DelBuckets()
  in other cases, it will close the bucket instance once the bucket
  information is obtained.

Change-Id: Ia75a7b88c66809374ccb6c4e42920cba7c3536ca
Reviewed-on: http://review.couchbase.org/42461
Reviewed-by: John Liang <johliang00@gmail.com>
Reviewed-by: Pratap Chakravarthy <prataprc@couchbase.com>
Tested-by: Pratap Chakravarthy <prataprc@couchbase.com>