Add a check to ui_SystemTray test to make sure it is only being run on link

A few people have being getting failures for this test by running it on
invalid boards. This makes sure that the test exists if not run on link.

BUG=chrome-os-partner:41512
TEST=test_that -b <notlink> ip ui_SystemTray

Change-Id: I97098adc8043fda8d95c2f0ae6b96476f4d7bf48
Reviewed-on: https://chromium-review.googlesource.com/281398
Tested-by: David Haddock <dhaddock@chromium.org>
Reviewed-by: Mussa Kiroga <mussa@chromium.org>
Commit-Queue: David Haddock <dhaddock@chromium.org>
1 file changed