Fixed race condition: err "the pool is closed" during a rebalance
Fixed race condition: err "the pool is closed" during a rebalance

Commit from go-couchbase:
If Bucket.Do obtains a connection pool at the same time that another
goroutine refreshes the bucket's vbucket map, the bucket can end up with
an already-closed pool which will return errors trying to get a
connection.
Added a utility method Bucket.getConnectionToVBucket that does this
safely by retrying if it got a closed connection pool.

tleyden/sync_gateway,ceejatec/sync_gateway,evankyle/sync_gateway,jamiltz/sync_gateway,evankyle/sync_gateway,jamiltz/sync_gateway,ceejatec/sync_gateway,tophatch/sync_gateway,paulharter/sync_gateway,couchbaselabs/sync_gateway,tleyden/sync_gateway,tophatch/sync_gateway,paulharter/sync_gateway,ceejatec/sync_gateway,tleyden/sync_gateway,tophatch/sync_gateway,paulharter/sync_gateway,tophatch/sync_gateway,couchbaselabs/sync_gateway,ceejatec/sync_gateway,evankyle/sync_gateway,paulharter/sync_gateway,couchbaselabs/sync_gateway,tleyden/sync_gateway,couchbaselabs/sync_gateway,jamiltz/sync_gateway,evankyle/sync_gateway