With this commit, pushes to branches can trigger tests directly on
Github Actions.

Here it will be able to test against kernel 4.14 and 5.0.0, which correspond
to the latest Ubuntu LTS kernel releases.

Tests are run for both Debug and Release modes.

Tests run inside docker, in an ubuntu 19.04 container base.

For the github workflow:

- The test_libbcc suite is run first, to potentially fail fast on these faster
unit tests.
- The Python test suite is run

Some of these tests are allowed to fail, but the failure is still reported:

- In catch2 tests, using the [!mayfail] tag, where this will be displayed in
the test summary
- In Python unittests, using the `@mayFail("Reason")` decorator, which is
introduce for consistency with catch2. These will report the reason for the
failure, and log this to an artifact of the test.