TestServerDuplicateBackgroundRead has been causing crashes on the
netbsd-arm-bsiegert builder, with the system becoming completely
unresponsive (probably deadlocked). Skip this test while the crash
is under investigation.

Upstream bug report is http://gnats.netbsd.org/53173.

Change-Id: Ib48f19005cf2cbba8a27e75e689c2acb025d8870
Reviewed-on: https://go-review.googlesource.com/106295
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>