FIX replace nose with pytest for Python 3.10 compatibility

[xcompass]

nose 1.3.7 is abandoned and incompatible with Python 3.10 (removed collections.Callable). Replace nosetests with pytest in Makefile targets (testb, testb-coverage, testb-profile, testci) and swap nose==1.3.7 for pytest + pytest-cov in requirements.txt.

[xcompass]

won't have time to test it before I'm off. Please test it before merge.

[catinhere]

Tested locally and inside container. BE tests are running fine with pytest.

There are currently two test failures:

• test_create_attachment in test_file.py: due to change in 0734c58. uuid and filename are not the same anymore
• test_saml_metadata in test_file.py: only fails running inside container because SAML_METADATA_URL="https://samltest.id/saml/idp", which no longer exists. Perhaps we should mock the response returned from OneLogin_Saml2_IdPMetadataParser.parse_remote

Above tests will be updated in another PR