Tests should use CTest

[sithhell]

We currently rely on a custom testing script. CMake provides an extensive framework for running tests. This includes a nice dashboard to see which tests failed.

[hkaiser]

Before this change it was possible to pass arbitrary arguments to all tests by saying:

make HPX_TEST_ARGUMENTS=<...>  tests

This functionality was very useful for instance to force the tests to use a specific parcel port or similar.

[sithhell]

Good point. I missed that during the switch.

[hkaiser]

I think we need to pass any additional arguments using hpx_run_tests.py ... --args <...>

[sithhell]

Works again.