net: skip unsupported tests on iOS
net: skip unsupported tests on iOS

The new iOS test harness forwards environment variables, such that
tests that skipped on non-builders now run because GO_BUILDER_NAME
is set.

Skip the net tests that rely on resolv.conf being present.

Change-Id: I7875dc4252b2ab696c9aae13a9106ddf296ee8ec
Reviewed-on: https://go-review.googlesource.com/111476
Run-TryBot: Elias Naur <993af7099cb24ce1a88d64108ae1e8b0385f2fc0@gmail.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

nawawi/go,josharian/go,cloudflare/go,golang/go,akutz/go,josharian/go,nawawi/go,nawawi/go,CAFxX/go,CAFxX/go,CAFxX/go,cloudflare/go,CAFxX/go,nawawi/go,cloudflare/go,CAFxX/go,golang/go,akutz/go,cloudflare/go,cloudflare/go,cloudflare/go,akutz/go,golang/go,josharian/go,golang/go,nawawi/go,golang/go,CAFxX/go,josharian/go,akutz/go,golang/go,josharian/go,akutz/go,cloudflare/go,akutz/go,nawawi/go,josharian/go,golang/go,akutz/go,akutz/go,nawawi/go,josharian/go,cloudflare/go,CAFxX/go,josharian/go,nawawi/go,golang/go,CAFxX/go