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_software_config.py b/scenario/test_server_software_config.py
index ec12fda..df35042 100644
--- a/scenario/test_server_software_config.py
+++ b/scenario/test_server_software_config.py
@@ -42,6 +42,13 @@
 
 class SoftwareConfigIntegrationTest(scenario_base.ScenarioTestsBase):
 
+    def setUp(self):
+        super(SoftwareConfigIntegrationTest, 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 = self.stack_identifier
         # Check that all stack resources were created