add a way for callback to disable itself

The idea is that some plugin would not be called in some
specific case, and the callback should decide by itself.

Having a way to globally disable it is much cleaner than
disabling every method one by one on the plugin side.

My use case is for fedora-infrastructure that cannot be run
from git checkout since it try to connect to the message bus,
but another case would be to bootstrap infrastructure, or to
run the code on a test servers without having all the callback
infrastructure setup.
add test for the disabling of callback plugins
switch to DictCursor
Template sudo_user via with_items
Fix 'hg module fails with: AttributeError: 'AnsibleModule' object has no attribute 'parames''
Fix Hg.__init__(...) reading value from self.hg_path
Merge pull request #4432 from madsweitling/devel

Fix typo and broken "Hg.__init__" in 'hg' module
toned down the error message for unconfigured master/slave
Implement a |changed filter plugin
make changed filter understand results lists
Merge pull request #4437 from sergevanginderachter/changed_filter

Implement a |changed filter plugin
Remove examples of module antipattern of setting the choices array for boolean types.
Fixes #4312 for older versions of usermod which do not have --append
Add missing version_added doc to mysql login port parameter.
Merge pull request #4342 from pileofrogs/devel

mysql_replication switch to DictCursor for compatibility with more mysql server versions
GH-4452 Corrected config load order to match docs with

cwd > ~ > /etc

Signed-off-by: Philip Schwartz <philip.schwartz@rackspace.com>
This oneliner change allows apt-key to inherit the http_proxy variable.

Before this fix

  TASK: [apt_repository repo='ppa:vbernat/haproxy-1.5'] *************************
  failed: [134.226.115.202] => {"cmd": ["apt-key", "adv", "--recv-keys", "--keyserver", "keyserver.ubuntu.com", "CFFB779AADC995E4F350A060505D97A41C61B9CD"], "failed": true, "rc": 2}
  stderr: gpg: requesting key 1C61B9CD from hkp server keyserver.ubuntu.com
  gpg: no valid OpenPGP data found.
  gpg: Total number processed: 0

After the fix

  TASK: [apt_repository repo='ppa:vbernat/haproxy-1.5'] *************************
  changed: [134.226.115.202]
Merge pull request #4453 from pschwartz/fix_cfg_load_order_to_match_docs

GH-4452 Corrected config load order to match docs
Merge pull request #4456 from jcftang/devel

This oneliner change allows apt-key to inherit the http_proxy variable.
Fixed crash when s3 bucket did not exist for put operation