TestRTC: Improve mic test by adding fail criteria based on input volume and also active input channel detection.

Added testing of input channels to determine how many are active and display the volume.
Added validation of the input volume, if its too low fail the test.
What about using 0 as buffer Size? or can you add an explanation why do you need a 4016? Maybe to get more frames to be captured for testing?

From W3C web-audio:
"If it's not passed in, or if the value is 0, then the implementation will choose the best buffer size for the given environment " (...) "It is recommended for authors to not specify this buffer size and allow the implementation to pick a good buffer size to balance between latency and audio quality."