Add tests for Azure spot instance

[zpoint]

Test case for: #4423

Add test case: test_azure_spot_instance_verification

Test Azure spot instance provisioning with explicit verification.
    This test verifies that when --use-spot is specified for Azure:
    1. The cluster launches successfully
    2. The instances are actually provisioned as spot instances

Tested (run the relevant ones):

• Code formatting: bash format.sh
• Any manual or new tests for this PR (please specify below)
• All smoke tests: pytest tests/test_smoke.py
• Relevant individual smoke tests: pytest tests/test_smoke.py::test_fill_in_the_name
• Backward compatibility tests: conda deactivate; bash -i tests/backward_compatibility_tests.sh

[zpoint]

/pre-merge-test

[Michaelvll]

LGTM. Thanks @zpoint!