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>
Modifying host configuration like this makes me really nervous, it could cut off access to host if something goes wrong.  IMHO, it's okay to just list these changes as a pre-req. in docs, or could we workaround it another way?