CTest: forwarding command-line arguments to test executables

This is a feature request for being able to forward command-line arguments to test executables when calling CTest.

For example: ctest --custom-arguments <arguments> should call each test executable with <arguments> command-line arguments.

Currently it requires ugly work-arounds: https://stackoverflow.com/questions/28812533/how-to-pass-command-line-arguments-in-ctest-at-runtime

This feature is helpful when porting existing test runners with rich CLIs to CTest.