WIP: Asyncio in run tests script

[rwols]

Only tested for Linux and tested locally. So my expectation is that the CI will fail.
This branch should evolve more.

I have also replaced the polling behavior to check whether the UnitTesting plugin is loaded by a UnitTestingSchedulerPingCommand class. The run_tests.py script calls this command via subl --command unit_testing_scheduler_ping. Once UnitTesting is loaded, that command will write to a flie. In run_tests.py we check whether that file exists. If it exists, then we know that UnitTesting is loaded.

[rwols]

The py versions are too old in the docker images :)

[randy3k]

Thank you for working on it. I wanted to rewrite the script for a long time. We use a different file run_tests.ps1 for windows. That one needs to be patched too.

[rwols]

How attached are you to the run_tests.ps1 script? Would it be possible to run run_tests.py in a windows environment as well? Because we're running a TCP server in run_tests.py and I don't know how to achieve that in Powershell. Other than calling the run_tests.py script from run_tests.ps1.

[randy3k]

Actually, the windows support was mainly contributed by @guillermooo. I personally do not have any preference. Actually, it may be easier for a maintenance point of view if any platform uses the same code.

It may be a good time to introduce some breakage when ST4 is out.