[Bug 39512] Make it possible to run multiple tests in a single task

https://bugs.winehq.org/show_bug.cgi?id=39512

--- Comment #2 from François Gouget  ---
The situation has changed a bit since the bug was opened:
* Merging TestLauncher and WineTest is no longer a goal.
* The TestBot now creates a single job no matter how many test modules (aka dll
or program) have been modified which cuts down on the number of build tasks
(only a small improvement from the too many tasks point of view).

So another solution that would not require special WineTest builds would be to
simply upload all the test binaries, TestLauncher, and then send a batch file
that runs TestLauncher for each test unit in sequence.

TestLauncher enforces the test unit timeout in the same way as WineTest so this
would not be so different. There is also less risk of ending up with a bloated
test binary with TestLauncher. In particular we would not be downloading the
extra WineTest code from the build VM for each job.