Update shared conformance tests

[tseaver]

We need to add a test suite which exercises the cross-language tests and fix anything where we don't pass.

We need to update the shared conformance tests to match the current spec:

• Proto spec for the testcase file
• Testcase file

/cc @frankyn

[frankyn]

@tseaver I misunderstood this file -> https://github.com/googleapis/python-storage/blob/master/tests/unit/url_signer_v4_test_data.json

I understood this JSON file as being the cross-language conformance tests.

[tseaver]

Hmmm, looks like that is conformance tests. Dunno how I missed that they existed already. Looks like an older version of the file?

[frankyn]

+1, I recently changed the schema and added conformance tests for Signed Policies.

[tseaver]

Suggested implemenation plan:

• Move the test drivers for signing out into a separate file, like the test_cross_language.py file in python-firestore.
• Rename the data file to match the upstream name (v4_signatures.json).
• Copy in the new test data file, update the test drivers to match the new schema, if needed, and fix anything broken.
• Add a test driver for the Signed Policy testcases.

[tseaver]

I have a branch which implements the first two steps cleanly, and a stash for the third one, where some of the tests no longer pass. Actually landing the new tests is going to need to wait for PRs #48 and #56 to land, I think.

[frankyn]

@HemangChothani, @tseaver is tracking conformance test updates in here. Referenced issues are merged/unblocked.

[frankyn]

This was fixed by @IlyaFaer