[FSTORE-1183] Error downloading credentials for Kafka storage connector in Python mode

[bubriks]

This PR adds/fixes/changes...

• please summarize your changes to the code
• and make sure to include all changes to user-facing APIs

JIRA Issue: -

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How Has This Been Tested?

• Unit Tests
• Integration Tests
• Manual Tests on VM

Checklist For The Assigned Reviewer:

- [ ] Checked if merge conflicts with master exist
- [ ] Checked if stylechecks for Java and Python pass
- [ ] Checked if all docstrings were added and/or updated appropriately
- [ ] Ran spellcheck on docstring
- [ ] Checked if guides & concepts need to be updated
- [ ] Checked if naming conventions for parameters and variables were followed
- [ ] Checked if private methods are properly declared and used
- [ ] Checked if hard-to-understand areas of code are commented
- [ ] Checked if tests are effective
- [ ] Built and deployed changes on dev VM and tested manually
- [x] (Checked if all type annotations were added and/or updated appropriately)

[SirOibaf]

I really don't understand this regex. A hopsworks path can either start with / or hdfs:// (or hopsfs:// for that matter), but for sure not with dfs:// - So I'm really not sure why we are checking if it begins with dfs://

If I try the regex in a Python interpreter it doesn't match the following string: hdfs:///apps/hive/warehouse/test which is a problem considering that here:

feature-store-api/python/hsfs/engine/python.py

Line 905 in 2cd5b2f

file = "hdfs://" + file

we add hdfs:// at the beginning of the file if the file doesn't contain any scheme.

I also checked a couple of storage connector, the rest API doesn't return any scheme, meaning hdfs:// is added by the line above.

This also means, that the default behaviour of uploading the credentials in the storage connector directory within the Hive warehouse directory is now broken with this PR because the regex doesn't match hdfs://.

When you test this PR, please test both cases.

[bubriks]

yeah sorry i am not sure how i lost the h from hdfs and probably didnt catch it because of this if statement: https://github.com/logicalclocks/feature-store-api/blob/master/python/hsfs/engine/python.py#L908 (aka. don't download file if it already exists)