Drain the socket when updater is stopped

The socket might still contain data that was retreived when the updater
was still running. This will confuse further requests if the data is
not drained from the socket.

Change-Id: I0be0a123f4d26f359317712fe2d11580881409a5
Reviewed-on: http://review.couchbase.org/33746
Reviewed-by: Filipe David Borba Manana <fdmanana@gmail.com>
Tested-by: Volker Mische <volker.mische@gmail.com>