Move installation steps to YAML filex

- move installation steps to YAML files
- add fixtures and snapshots for install salt, common services
  and openstack
- fixtures in conftest.py now are included by python instead of
  using pytest plugins
diff --git a/tcp_tests/helpers/ext.py b/tcp_tests/helpers/ext.py
index 5369535..9147fb8 100644
--- a/tcp_tests/helpers/ext.py
+++ b/tcp_tests/helpers/ext.py
@@ -36,8 +36,9 @@
 SNAPSHOT = enum(
     'hardware',
     'underlay',
-    'tcp_deployed',
-    'os_deployed',
+    'salt_deployed',
+    'common_services_deployed',
+    'openstack_deployed',
 )
 
 LOG_LEVELS = enum(