The permissions on this file should be 0440

The permissions are 0440 on a standard build of at least Ubuntu and CentOS.
Having them changed to 0400 means they get flipped on every Puppet run (set
correctly and then incorrectly by this module) and then when logging in as sudo
are set back correctly.
Update test for new permission
Merge pull request #10 from alphagov/master

Change permissions on /etc/sudoers to be the same as standard build