[autotest] audio_test_utils: Add callback to monitor_no_nodes_changed

Add a callback so test can dump logs when there is unexpected
NodesChanged signal.

BUG=chromium:547100
TEST=not used yet.

Change-Id: I12195ba9b96b0a82e5c6a53f4683f9b487886f25
Reviewed-on: https://chromium-review.googlesource.com/312080
Commit-Ready: Cheng-Yi Chiang <cychiang@chromium.org>
Tested-by: Cheng-Yi Chiang <cychiang@chromium.org>
Reviewed-by: Kalin Stoyanov <kalin@chromium.org>
1 file changed