There's another test that opens an hard-coded port to talk to debugserver
(TestPlatformSDK.py). Make sure this port and the one in that other
test are different to avoid that potential conflict.
We weren't setting the listener back to the unhijacked one in this
case, so that a continue after the stop fails. It thinks the process
is still running. Also add tests for this behavior.
Differential Revision: https://reviews.llvm.org/D112747