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/command.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 import constants as C
+from ansible.plugins.action import ActionBase
+from ansible.utils.vars import merge_hash
+
+
+class ActionModule(ActionBase):
+
+    def run(self, tmp=None, task_vars=None):
+        self._supports_async = True
+        results = super(ActionModule, self).run(tmp, task_vars)
+
+        # Command module has a special config option to turn off the command nanny warnings
+        if 'warn' not in self._task.args:
+            self._task.args['warn'] = C.COMMAND_WARNINGS
+
+        wrap_async = self._task.async_val and not self._connection.has_native_async
+        results = merge_hash(results, self._execute_module(tmp=tmp, task_vars=task_vars, wrap_async=wrap_async))
+
+        return results