dockertest.fake_docker_api: Simple implementation of python-docker-py

This module is intended for faking some of python-docker-py classes
for docker-autotest testing purposes. This version supports
docker.client.Client with "version" method.

Signed-off-by: Lukáš Doktor <ldoktor@redhat.com>
subtests..version: Use fake_docker_api to get version string

Use dockertest.fake_docker_api instead of custom HTTP request
when python-docker-py is not available.

Signed-off-by: Lukáš Doktor <ldoktor@redhat.com>