[21.01] Use keep_original in pysam.tabix_index to not remove original data

[mvdbeek]

What did you do?

• Use keep_original in pysam.tabix_index to not remove original data

Without this you can take a VCF dataset, switch it to VcfGz, and then see that the source dataset is gone (it's now compressed at source_dataset_path.gz).

Why did you make this change?

Had an odd case of a disappearing dataset from a data library reported.

How to test the changes?

(select the most appropriate option; if the latter, provide steps for testing below)

• I've included appropriate automated tests.
• This is a refactoring of components with existing test coverage.
• Instructions for manual testing are as follows:
  take a VCF dataset, switch it to VcfGz, and then see that the source dataset is not gone

License

• I agree to license these contributions under Galaxy's current license.
• I agree to allow the Galaxy committers to license these and all my past contributions to the core galaxy codebase under the MIT license. If this condition is an issue, uncheck and just let us know why with an e-mail to galaxy-committers@lists.galaxyproject.org.

For UI Components

• I've included a screenshot of the changes