Some servers return a websocket url without a port. This patch
automatically adds :80 for ws and :443 for wss.

Change-Id: Ifdcdbda8f87c994a5f351234c83bf4a07be34ea2
Reviewed-on: https://go-review.googlesource.com/2210Reviewed-by: Mikio Hara <mikioh.mikioh@gmail.com>