Use the existing GPG fixture in the functional tests (CryptoUtil 2/3) by nabla-c...

Status

Ready.

Description of Changes

This PR updates the functional tests to use the same fixture for GPG as the other tests. It also updates the config fixture.

• This is a prerequisite for the refactoring of the GPG code in #6160 which uses the updated config fixture.
• This is a small step forward for #3836. More work is needed to refactor the functional tests and their fixtures.
• Because the GPG fixture that is now being used is session-scoped, it is only called once during the whole test suite, and only one GPG home directory is used for all the tests. This helps a little bit with #4332 (only 1 GPG process should get created instead of ~80).
• There is more work to be done with the config fixture itself, and I might take a look at it eventually. The biggest problem is that tests might either use the config from the config() fixture, or the config from the config.py file generated by make test right before the tests run.
  • This creates really tricky interactions and bugs when working on the test suite, because it's unclear which config is being used. It's also sometime unclear what config is needed for a specific test to succeed, and some tests also tend to mutate the config object (for example changing the time it takes for a session to expire).
  • This PR makes small changes to slightly improve this situation.