This changes most of the tests to use minimal image. There are
now two tests left that use fedora image.
[1] SoftwareConfigIntegrationTest.test_server_software_config
[2] CfnInitIntegrationTest.test_server_cfn_init
Out of which [1] is already disabled at the gate.
Change-Id: I309989de1e5584f3e345213c4b62893159365973
Related-Bug: #1628302