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>
If the docker daemon is ever left in a broken state, it will affect **every** following test.  It would be nice to have some more assurance it is really restarted.  How about a ``try...finally`` here in case something in the ``remove_after_test`` part breaks?