Search path (#16387)

* smarter function to figure out relative paths

takes list of paths in order of relevance to current task
and does the dwim magic on them

* shared function for action plugins using new dwim

unify path construction and error info/messaging
made include and role non exclusive
corrected order and now smarter about tasks
includes inside roles are currently broken as they don't provide the correct role data
make dirname full match to avoid corner cases

* migrated action plugins to new dwim function

reported plugins to use exceptions instead of info

* clarified needle

lib/ansible/plugins/action/__init__.py

@@ -823,3 +823,31 @@ class ActionBase(with_metaclass(ABCMeta, object)):
                 diff["after"] = " [[ Diff output has been hidden because 'no_log: true' was specified for this result ]]"
 
         return diff
+
+    def _find_needle(self, dirname, needle):
+        '''
+            find a needle in haystack of paths, optionally using 'dirname' as a subdir.
+            This will build the ordered list of paths to search and pass them to dwim
+            to get back the first existing file found.
+        '''
+
+        path_stack = []
+
+        dep_chain =  self._task._block.get_dep_chain()
+        # inside role: add the dependency chain
+        if dep_chain:
+            path_stack.extend(reversed([x._role_path for x in dep_chain]))
+
+
+        task_dir = os.path.dirname(self._task.get_path())
+        # include from diff directory: add it to file path
+        if not task_dir.endswith('tasks') and task_dir != self._loader.get_basedir():
+            path_stack.append(task_dir)
+
+        result = self._loader.path_dwim_relative_stack(path_stack, dirname, needle)
+
+        if result is None:
+            raise AnsibleError("Unable to find '%s' in expected paths." % needle)
+
+        return result
+