Provide a way to cancel the test runner

[rwols]

We're getting at around 200 tests now for LSP and we have a ton of yield lambda: condition() in setUp and tearDown methods. It can take a long time to wait for UnitTesting to finish if every one of those setUp methods fail to await the condition.

[rwols]

I know that "failfast" exists for unittesting.json but it would be nice to keep that set at False and cancel the test runner via the command palette.

[deathaxe]

All settings available in unittesting.json can also be passed to the commands and take precedence.

Adding the following to Default.sublime-commands would provide a test command, which always fails on first caught exception.

  {
    "caption": "UnitTesting: Test Current Package (Fail Fast)",
    "command": "unit_testing_current_package",
    "args": {"failfast": true},
  },