Follow up to #70221
Related to #67794
CVE-2020-1736
When set_mode_if_different() is called with mode of 'None', ensure we issue
a warning about the change in default permissions.
Add integration tests to ensure the warning works properly.
* Fix tests
- actually use custom module 🤦♂️
- verify file permission on created files
- use remote_tmp_dir so we're ready for split controller
- improve test module so we can skip the call to set_fs_attributes_if_different()
- fix tests for CentOS 6
