This test is the only remaining one that does not use gtest and that's
blocking some infra cleanup tasks. Ideally this test would use
webrtc/rtc_base/flags.h but that's a lot of unnecessary work.
This also replaces some exit() status codes - the logic behind this is
if you get incorrectly specified command line arguments, exit(1) is
invoked for a failure, because it's not a test failure, and if flag
parsing was done properly, it would not be a gtest failure anyway.
BUG=webrtc:7568
Review-Url: https://codereview.webrtc.org/3000033002
Cr-Commit-Position: refs/heads/master@{#19388}