We couldn't copy to_unicode, to_bytes, to_str into module_utils because
of licensing. So once created it we had two sets of functions that did
the same things but had different implementations. To remedy that, this
change removes the ansible.utils.unicode versions of those functions.
* Rm py2.7+ code in docker connection plugin
The docker connection plugin was using subprocess.check_output
which only exists in python 2.7 and later. Connection plugins
need to support python2.6 so this replaces it with Popen/communicate()
* Handle docker ver errors in docker connection
Add unit tests for DockerConnection
Fixes#16971
Also making PlayContext a child class of the Playbook Base class,
which gives it access to all of the FieldAttribute code to ensure
field values are correctly typed after post_validation
Fixes#11381
