Synchronous adb shell and pull for loopback start script

Before the removal and copy of script of video file on the android
device was done asynchronously, which was a bug.

BUG=webrtc:6545
NOTRY=True

Review-Url: https://codereview.webrtc.org/2470663004
Cr-Original-Commit-Position: refs/heads/master@{#14898}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 3e79dbdc377807972a15bd9172ed4d25e7a27d55
1 file changed