Remove shell module specialcases

Shell is implemented via the command module.  There was a special case
in mod_args to do that.  Make shell into an action plugin to handle that
instead.

Also move the special case for the command nanny into a command module
action plugin.  This is more appropriate as we then do not have to send
a parameter that is only for the command module to every single module.

lib/ansible/plugins/action/shell.py

@@ -0,0 +1,25 @@
+# Copyright: (c) 2017, Ansible Project
+# GNU General Public License v3.0+ (see COPYING or https://www.gnu.org/licenses/gpl-3.0.txt)
+
+from __future__ import (absolute_import, division, print_function)
+__metaclass__ = type
+
+from ansible.plugins.action import ActionBase
+from ansible.utils.vars import merge_hash
+
+
+class ActionModule(ActionBase):
+
+    def run(self, tmp=None, task_vars=None):
+        # Shell module is implemented via command
+        self._task.action = 'command'
+        self._task.args['_uses_shell'] = True
+
+        command_action = self._shared_loader_obj.action_loader.get('command',
+                                                                   task=self._task,
+                                                                   connection=self._connection,
+                                                                   play_context=self._play_context,
+                                                                   loader=self._loader,
+                                                                   templar=self._templar,
+                                                                   shared_loader_obj=self._shared_loader_obj)
+        return command_action.run(task_vars=task_vars)