change pytest fixture scopes to 'session' and add tmpdir methods if required

[cadeduckworth]

MDPOW/mdpow/tests/test_automated_dihedral_analysis.py

Line 35 in 8ac9549

@pytest.fixture(scope="function")

• link to test cleanup PR once 217 is merged, review all test modules
• review and update all tests pertaining to EnsembleAnalysis - related modules

[orbeckst]

See also #194 — remove bundled tempdir whenever you come across it...

[cadeduckworth]

also remove function specification where the scope is not going to be changed

[cadeduckworth]

https://docs.pytest.org/en/6.2.x/fixture.html