audio_settings script would fail on Vivid

While testing the audio playback job with the following command:
plainbox run -i "2013.com.canonical.certification::audio/playback_auto"

It will fail with the following error:

Traceback (most recent call last):
  File "/tmp/nest-xhm2dm1q.31fe8937351983f9ecce53888ec8d0346fca5a4673471fa7e36e25ea11245065/audio_settings", line 9, in <module>
    sys.exit(main())
  File "/usr/lib/python3/dist-packages/checkbox_support/scripts/audio_settings.py", line 363, in main
    store_audio_settings(settings_file)
  File "/usr/lib/python3/dist-packages/checkbox_support/scripts/audio_settings.py", line 217, in store_audio_settings
    default = default_regex.search(pactl_status).group()
AttributeError: 'NoneType' object has no attribute 'group'
Attempting to initialize Gstreamer pipeline: audiotestsrc wave=sine freq=512 ! audioconvert ! audioresample ! autoaudiosink
Pipeline initialized, now starting playback.
ERROR:root:Unable to restore settings because settings file is invalid

Version information
ubuntu@201304-13197:~$ apt-cache policy checkbox
checkbox:
  Installed: (none)
  Candidate: 0.18-0ubuntu2
  Version table:
     0.18-0ubuntu2 0
        500 http://archive.ubuntu.com/ubuntu/ vivid/universe amd64 Packages
ubuntu@201304-13197:~$ apt-cache policy plainbox
plainbox:
  Installed: 0.22+bzr3819+pkg29~ubuntu15.04.1
  Candidate: 0.22+bzr3819+pkg29~ubuntu15.04.1
  Version table:
 *** 0.22+bzr3819+pkg29~ubuntu15.04.1 0
        500 http://ppa.launchpad.net/checkbox-dev/ppa/ubuntu/ vivid/main amd64 Packages
        100 /var/lib/dpkg/status
     0.5.4-1 0
        500 http://archive.ubuntu.com/ubuntu/ vivid/universe amd64 Packages
ubuntu@201304-13197:~$ plainbox dev list provider
provider '2013.com.canonical.plainbox:manifest'
provider '2013.com.canonical.plainbox:categories'
provider '2013.com.canonical.certification:certification-client'
provider '2013.com.canonical.certification:checkbox'
provider '2013.com.canonical.certification:plainbox-resources'

BTW, I think zyga did mentioned about this before when reviewing my BT-A2DP test case.
Please refer to https://code.launchpad.net/~cypressyew/checkbox/bt-a2dp-fix/+merge/258860