Fix apt default integration test

[TheRealFalcon]

The apt default test wasn't ported over from cloud-tests correctly.
Fix it so it works as it did in the cloud tests.

Also add openstack specific test for apt configuration with no uri.

Proposed Commit Message

Fix apt default integration test

The apt default test wasn't ported over from cloud-tests correctly.
uri should be specified in the test, but it was not, so the test
failed on openstack (and likely other platforms) because without
a specified uri, the default uri will vary by platform. I separated
this uri test out into a separate test function.

Also add openstack specific test for apt configuration with no uri.
Other platform-specific tests should be added here over time.

Additional Context

n/a

Test Steps

Run integration tests on openstack

Checklist:

• My code follows the process laid out in the documentation
• I have updated or added any unit tests accordingly
• I have updated or added any documentation accordingly

[OddBloke]

Some information in the commit message about how the porting was incorrect would be good: I'm struggling to determine what here is remedial, and what is new testing.

[OddBloke]

Don't think we need this?

[OddBloke]

Could we use cloud-init query v1.availability_zone here instead?

[OddBloke]

Generalising it is out-of-scope for this PR, but if we do, can this test run on more than just OpenStack? We perform region/AZ substitution on every cloud; an EC2 instance I have kicking around, for example:

deb http://eu-west-1.ec2.archive.ubuntu.com/ubuntu/ focal main restricted

[TheRealFalcon]

Yep, I noticed there there were different templates for different clouds, so I figured we would want multiple versions, but since I was just testing on openstack, I started with openstack.

[TheRealFalcon]

I updated the commit message on the PR (not in the actual commit). Is that enough context?

[OddBloke]

Thanks, exactly what I needed. Confirmed that these tests pass locally.