/etc/services is not available on Android. The pure Go implementation
of LookupPort will never succeed on Android. Skipping the test.

Updates #14576.

Change-Id: I707ac24aea3f988656b95b1816ee5c9690106985
Reviewed-on: https://go-review.googlesource.com/20154Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>