Test cases in checkbox-converged won't be excuted in the expected order

[Po-Hsu Lin]

Step:
1. Select the 14.04 test plan and start testing
2. Check if it's testing in the following order:
    audio/speaker-headphone-plug-detection
    audio/microphone-plug-detection
    audio/playback_headphones
    audio/alsa_record_playback_external
    audio/playback_auto
    audio/alsa_record_playback_internal
    audio/alsa_record_playback_automated

Expected result:
* Test case executed in the expected result, as listed in the test plan

Actual result:
* It's not executed in the expected order.