pytests: Add conftest.py and other tests

[prashant1221]

conftest.py contain common fixtures to setup and teardown. We use them wherever feasible

Added Configurations and Hardware section tests in tests_all_configs. It tests the keys present under those section in our config file.

pytest/test_raw_image_option.py checks .img if provided instead of vmdk should still work. After that it matches values for the same in ovf and our yaml.