Add dataset tests

[sphamba]

Prework

• [x] I understand and agree to this repository's code of conduct.
• [x] I understand and agree to this repository's contributing guidelines.
• [x] I have already submitted an issue or discussion thread to discuss my idea with the maintainers.

What kind of change does this PR introduce? (check at least one)

• [ ] Bugfix
• [x] Feature
• [ ] Documentation
• [ ] Tutorial
• [ ] Code style update
• [ ] Refactor
• [ ] Build-related changes
• [ ] Other, please describe:

Does this PR introduce a breaking change? (check one)

• [ ] Yes
• [x] No

If yes, please describe the impact and communicate accordingly:

The PR fulfills these requirements:

• [ ] It's submitted to the branch named as follow :
  • Fix a bug: bugfix-<some_key>-<word>
  • Improve the doc: doc-<some_key>-<word>
  • Improve a tutorial tutorial-<some_key>-<word>
  • Add a new feature: feature-<some_key>-<word>
  • Refactor some code: refactor-<some_key>-<word>
  • Optimize some code: optimize-<some_key>-<word>
• [ ] When resolving a specific issue, it's referenced in the PR's title (e.g. fix #xxx[,#xxx], where "xxx" is the issue number)
• [ ] Don't forget to link PR to issue if you are solving one.
• [ ] All tests are passing.
• [x] New/updated tests are included

If adding a new feature, the PR's description includes:

• [x] A convincing reason for adding this feature (to avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it)

Summary

• add script to generate small hdf5 files from downloaded raw files, and netcdf files from open_granule.
  • [ ] does not seem to work with all raw files (eg IMERG)
  • [ ] relies on start_date to be added in product_def.yml for all products
• add tests for granule
  • [ ] test comparing small hdf5 files with saved netcdf file fails
• add tests for groups and variables

[coveralls]

coverage: 47.262% (+5.6%) from 41.632% when pulling 3514c12719b2cbde68709320fb831529da12f734 on EPFL-ENAC:add_dataset_tests into 2fc2e2b27032afc9ac1b048dabf12c04d12cc6eb on ghiggi:main.