integration_tests: use unique MAC addresses for tests

[OddBloke]

Proposed Commit Message

integration_tests: use unique MAC addresses for tests

Using the same MAC address results in strange test behaviour if more
than one such instance is up: traffic gets routed to an arbitrary
interface with the given MAC address.  This can happen if running tests
in parallel, or on a system which retains test instances from previous
runs.

The introduction of tests/integration_tests/__init__.py means that
pylint now checks the integration tests: this commit also addresses
those failures.

Additional Info

This introduces tests/integration_tests/__init__.py as a holding place for the utility function this introduces; I didn't want to introduce a util, but it also didn't feel like it fit well in anything we currently had.

Test Steps

Run the affected tests in parallel a few times and observe a lack of collisions.

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

[TheRealFalcon]

Funny thing is I slightly prefer util.py to __init__.py. __init__.py has always seemed more "hidden" to me. But still +1 😄

[TheRealFalcon]

Did we turn up a setting on pylint? The pylint issues don't seem related to what you've changed.

[OddBloke]

Did we turn up a setting on pylint? The pylint issues don't seem related to what you've changed.

I suspect that adding __init__ means that pylint now recurses in when previously it didn't? I'll address them.