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>
In fact, it would even be okay IMHO to drop all the certificate stuff, and just have config. options pointing at the files.  It's a pain to set up, but you only need to do it one-time.  That would greatly reduce the amount of code and possible breakage points here as well.  Though it seems you put a lot of effort into it, so if you want to hang on to it that's okay too.