Add 'filtered' stdout callback plugin

This plugin filters output for any task that is 'ok' or 'skipped'.
It works by subclassing the 'default' stdout callback plugin and
overriding certain functions. It will suppress display of the task
banner until there is a 'changed' or 'failed' result or an
unreachable host.

lib/ansible/plugins/callback/filtered.py

@@ -0,0 +1,76 @@
+# (c) 2015, Andrew Gaffney <andrew@agaffney.org>
+#
+# This file is part of Ansible
+#
+# Ansible is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# Ansible is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with Ansible.  If not, see <http://www.gnu.org/licenses/>.
+
+# Make coding more python3-ish
+from __future__ import (absolute_import, division, print_function)
+__metaclass__ = type
+
+from ansible.plugins.callback.default import CallbackModule as CallbackModule_default
+
+class CallbackModule(CallbackModule_default):
+
+    CALLBACK_VERSION = 2.0
+    CALLBACK_TYPE = 'stdout'
+    CALLBACK_NAME = 'filtered'
+
+    def __init__(self):
+        self.super_ref = super(CallbackModule, self)
+        self.super_ref.__init__()
+        self.last_task = None
+        self.shown_title = False
+
+    def v2_playbook_on_task_start(self, task, is_conditional):
+        self.last_task = task
+        self.shown_title = False
+
+    def display_task_banner(self):
+        if not self.shown_title:
+            self.super_ref.v2_playbook_on_task_start(self.last_task, None)
+            self.shown_title = True
+
+    def v2_runner_on_failed(self, result, ignore_errors=False):
+        self.display_task_banner()
+        self.super_ref.v2_runner_on_failed(result, ignore_errors)
+
+    def v2_runner_on_ok(self, result):
+        if result._result.get('changed', False):
+            self.display_task_banner()
+            self.super_ref.v2_runner_on_ok(result)
+        else:
+            pass
+
+    def v2_runner_on_unreachable(self, result):
+        self.display_task_banner()
+        self.super_ref.v2_runner_on_unreachable(result)
+
+    def v2_runner_on_skipped(self, result):
+        pass
+
+    def v2_playbook_on_include(self, included_file):
+        pass
+
+    def v2_playbook_item_on_ok(self, result):
+        self.display_task_banner()
+        self.super_ref.v2_playbook_item_on_ok(result)
+
+    def v2_playbook_item_on_skipped(self, result):
+        pass
+
+    def v2_playbook_item_on_failed(self, result):
+        self.display_task_banner()
+        self.super_ref.v2_playbook_item_on_failed(result)
+