Use minimal image wherever possible

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
diff --git a/scenario/test_server_cfn_init.py b/scenario/test_server_cfn_init.py
index 7ed6082..c7d84e3 100644
--- a/scenario/test_server_cfn_init.py
+++ b/scenario/test_server_cfn_init.py
@@ -21,6 +21,10 @@
 
     def setUp(self):
         super(CfnInitIntegrationTest, self).setUp()
+        if not self.conf.image_ref:
+            raise self.skipException("No image configured to test")
+        if not self.conf.instance_type:
+            raise self.skipException("No flavor configured to test")
 
     def check_stack(self, sid):
         # Check status of all resources