subtests.docker_daemon: Adds tests for connection with certificate.

Tests generates certificates and sign them up with created CA certificate,
then test connect server and client part with different configurations.

Signed-off-by: Jiří Župka <jzupka@redhat.com>
I'd suggest giving it a different key-name (``cli_spec"?) since it works totally different from ``cli``, this way there is no question in the code which interface is being used.