Ability to ask testrunner ServerController to wait for server process exit and get the exit code

Imagine testing the shutdown --restart CLI command in a manualmode test.

The standalone.sh script is not used so the restart won't work, as the restart logic is in the script. But the test itself could handle the restart part if the ServerController would let it know when the server process is stopped and what the exit code was.

So,

1) test spawns a thread to do shutdown --restart in the CLI
2) test waits for server to stop, confirms correct exit code
3) test starts the server again
4) thread doing the shutdown --restart moves on since the server starts again