Reason for revert:
Enabling this again so we can start running it experimentally on the bots.
Original issue's description:
> Temporarily disable failing video_quality_loopback_test.py
>
> BUG=webrtc:7185
> TBR=mandermo@webrtc.org
>
> Review-Url: https://codereview.webrtc.org/2704073002 .
> Cr-Commit-Position: refs/heads/master@{#16697}
> Committed: 6951a28b41
TBR=mandermo@webrtc.org
BUG=webrtc:7185
NOTRY=True
Review-Url: https://codereview.webrtc.org/2734333002
Cr-Commit-Position: refs/heads/master@{#17110}