Add unit tests to audio_common (ros ticket #13)

[ahendrix]

There are currently no unit tests in audio_common.

Add at least basic unit tests to ensure that the API is stable and that method calls succeed.

trac data:

• Owner: ahendrix
• Reporter: ahendrix
• Reported at: Mon Sep 10 20:26:23 2012
• URL: https://kforge.ros.org/audiocommon/trac//ticket/13