Making WebRTC quality tests less dependent on installed tools.

This patch:
1) groups all tools for the audio and video quality tests per platform.
2) adds ffmpeg and zxing to the private tool bucket for all platforms.
3) updates the tests to the new tool locations.

This must land at the same time as a webrtc.DEPS CL which makes the
download step --recursive and --auto_platform for the private tool
bucket.

Left to fix:
1) The AQ test is still dependent on installed sox on mac/linux.

BUG=440387

Review URL: https://codereview.chromium.org/965403003

Cr-Commit-Position: refs/heads/master@{#318851}
155 files changed