Disable failing serial port tests on Android.

The tests are consistently failing on Android tablet testers.

TBR=reillyg@chromium.org

Bug: 928712
Change-Id: I2e4426f922a1966d13ced292f2beaaf2ae4f059e
Reviewed-on: https://chromium-review.googlesource.com/c/1454362
Reviewed-by: Rayan Kanso <rayankans@chromium.org>
Commit-Queue: Rayan Kanso <rayankans@chromium.org>
Cr-Commit-Position: refs/heads/master@{#629120}
1 file changed