Fix ordering for --diff mode setup

Due to the ordering of the vars passed to the _get_diff_data mode,
--diff mode would only work with --check activated, otherwise the file
used didn't exist and you would get an error similar to:

https://github.com/ceph/ceph-ansible/issues/2742

This PR allows this to work by configuring the diff data before running
the copy module, so the file exists.

Additionally, we should run with --diff mode enabled by default on tests
for this repository to ensure any functional issues with diff mode are
caught.

Change-Id: I020a181731c3ee87f04933f8c62213ea12cfa3a4

action/config_template.py

@@ -672,6 +672,9 @@ class ActionModule(ActionBase):
         # Content from config_template is converted to src
         new_module_args.pop('content', None)
 
+        # Set the diff data before running the copy module
+        _diff = self._get_diff_data(_vars['dest'], transferred_data, task_vars)
+
         # Run the copy module
         rc = self._execute_module(
             module_name='copy',
@@ -680,8 +683,7 @@ class ActionModule(ActionBase):
         )
         if self._play_context.diff:
             rc['diff'] = []
-            rc['diff'].append(self._get_diff_data(_vars['dest'],
-                                                  transferred_data, task_vars))
+            rc['diff'].append(_diff)
         if self._task.args.get('content'):
             os.remove(_vars['source'])
         return rc

tox.ini

@@ -34,6 +34,7 @@ setenv =
     ANSIBLE_LOOKUP_PLUGINS={toxinidir}/lookup
     ANSIBLE_STRATEGY_PLUGINS={toxinidir}/strategy
     ANSIBLE_LIBRARY={toxinidir}/library
+    ANSIBLE_PARAMETERS=--diff
 
 
 [testenv:docs]