HDF5: disable building test executables and running tests

[Roland Haas]

we never run the tests (they fail or take too long or create files too big) but still build them which also uses ~2GB of disk space and can lead to build failures when disk quota is tight.

Pull request is here: https://github.com/EinsteinToolkit/ExternalLibraries-HDF5/pull/4

[Roland Haas]

Please review.

[Roland Haas]

During ET call on 2021-09-02 http://lists.einsteintoolkit.org/pipermail/users/2021-September/008189.html @Yosef Zlochower approved giving it a try.

[Roland Haas]

Applied as git hash eeb204b "HDF5: disable building test executables and running tests" of ExternalLibraries-HDF5