Decouple H5 related self tests from large ATL03 data file

[jpswinski]

There are multiple self tests that expect the 2GB /data/ATLAS/ATL03_20200304065203_10470605_003_01.h5 file to be present on the system in order for the test to pass.

Instead there needs to be a very small (<1MB) example ATL03 file that is a part of the respository that is used for all of the self-tests.

The larger python based tests can place more expensive demands on what is present on the system because they are testing at an integrated system level.

At least the following files need to be updated:

• sliderule/scripts/tests/hdf5_file.lua
• sliderule/plugins/icesat2/tests/atl06_elements.lua

[jpswinski]

This has been completed. All self-tests in the sliderule repository have test data that is in the repository itself. All self-tests that required ATL03 data files have been moved to the sliderule-icesat2 plugin repository.