Remove jsonschema as a dependency

[Flavio Percoco]

The filesystem store uses jsonschema to parse the metadata files. While jsonschema does the validation job very well, I believe it's an unnecessary dependency for such a small validation to do and for such a small use-case.

I'd rather have this specific check done directly when accessing these values in python than having an extra dependency.

[Louis Taylor (kragniz)]

I don't have much of a preference on this. On the one hand, utilizing it rather than reinventing the wheel for checking the json format is probably better, and it's not a large overhead since a lot of openstack also has it as a dependency. As you say, though, we're basically using it to check two values in one place in the code, which seems like overkill:
    https://github.com/openstack/glance_store/blob/cb4c615e8495590983330b01c0cdaa272abf1181/glance_store/_drivers/filesystem.py#L72-82

[Ian Cordasco (icordasc)]

Yeah, I agree with everything Louis said. The block where it's actually used could definitely use a lot of re-factoring though.