This change replaces server tests with new ones that require features
introduced after go1 release, such as runtime-integrated network poller,
Dialer, etc.

Change-Id: Icf1f94f08f33caacd499cfccbe74cda8d05eed30
Reviewed-on: https://go-review.googlesource.com/9195Reviewed-by: Ian Lance Taylor <iant@golang.org>