test: Mock resolve_machine_ip() to compensate for FakeServerInfo missing attr

[slothkong]

Hey @pacospace,
The feature introduced in #138 brought in also a few broken unittests:

FAILED ewccli/tests/ewccli_infra_test.py::test_pre_delete_no_volumes - assert 1 == 0
FAILED ewccli/tests/ewccli_infra_test.py::test_pre_delete_non_ewccli_volumes - assert 1 == 0
FAILED ewccli/tests/ewccli_infra_test.py::test_pre_delete_ewccli_volume_detach_delete - assert 1 == 0
FAILED ewccli/tests/ewccli_infra_test.py::test_pre_delete_detach_failure - assert 'detach/delete failed' in "Unexpected error: 'FakeServerInfo' object has no attribute 'get'"

This PR addresses those 4 particular assertion failures.

What is new

• Added a mock for resolve_machine_ip() directly in the four tests so they only exercise the volume-detach procedure you care about.

Technical Note

FakeServerInfo doesn't totally mock the interface that pre_delete_server/resolve_machine_ip expect from server_info; it doesnt have a .get() method like the expected dict does.

A solution for the unittests would have also been to force FakeServerInfo to have a get() method, but that ties the tests to the implementation details of the code, which in general not a good practice we can avoid in this case.

[pacospace]

Thanks for this @slothkong, but this #142 covered also the issue you opened, so I think we can close this.