Make audiovideo_CRASFormatConversion not so flaky.

Fix the following issues:

1. Use fixed but different sine tones in the two audio streams at different
   sampling rate
2. Set output node volume level to 100

TEST=Run the test on stout and parrot.
BUG=chromium:307378

Change-Id: I36df3522f8b116f142d5147ffe2c71cbf399332d
Reviewed-on: https://chromium-review.googlesource.com/177430
Reviewed-by: Owen Lin <owenlin@chromium.org>
Tested-by: Owen Lin <owenlin@chromium.org>
Commit-Queue: Owen Lin <owenlin@chromium.org>
diff --git a/client/cros/audio/audio_helper.py b/client/cros/audio/audio_helper.py
index 7d9d0ad..7305b06 100644
--- a/client/cros/audio/audio_helper.py
+++ b/client/cros/audio/audio_helper.py
@@ -5,6 +5,7 @@
 
 import logging
 import os
+import pipes
 import re
 import shlex
 import subprocess
@@ -12,7 +13,6 @@
 import time
 
 from glob import glob
-
 from autotest_lib.client.bin import utils
 from autotest_lib.client.bin.input.input_device import *
 from autotest_lib.client.common_lib import error
@@ -484,3 +484,31 @@
 
     # If there is only one soundcard, return it, else return not found (None)
     return '0' if id == 1 else None
+
+def execute(args, stdin=None, stdout=None):
+    '''Executes a child command and wait for it.
+
+    Returns the output from standard output if 'stdout' is subprocess.PIPE.
+    Raises RuntimeError if the return code of the child command is not 0.
+
+    @param args: the command to be executed
+    @param stdin: the executed program's standard input
+    @param stdout: the executed program's stdandrd output
+    '''
+
+    ps = popen(args, stdin=stdin, stdout=stdout)
+    out = ps.communicate()[0] if stdout == subprocess.PIPE else None
+    returncode = ps.wait()
+    if returncode != 0:
+        raise RuntimeError( 'command failed(%d): %s' % (returncode, ps.command))
+    return out
+
+def popen(*args, **kargs):
+    '''Returns a Popen object just as subprocess.Popen does but with the
+    executed command stored in Popen.command.
+    '''
+    ps = subprocess.Popen(*args, **kargs)
+    the_args = args[0] if len(args) > 0 else kargs['args']
+    ps.command = ' '.join(pipes.quote(x) for x in the_args)
+    logging.info('Running: %s', ps.command)
+    return ps