adb_wait_for_device: Skip `adb wait-for-device`

This should still wait for the device to be attached and finished
booting, but will prevent no-output timeouts due to
`adb wait-for-device` never finishing.

The effect should be that, when an Android device is disconnected, the
"wait for device" step will run forever, or until the device
reconnects. This should prevent a disconnected device from spreading
purple all over the status page.

BUG=skia:

Review URL: https://codereview.chromium.org/1315753010
1 file changed