Add https cert and key options to docker

Docker-DCO-1.1-Signed-off-by: Colin L. Rice <colin@daedrum.net> (github: c00w)
Add https example

Docker-DCO-1.1-Signed-off-by: Colin L. Rice <colin@daedrum.net> (github: c00w)
Simplified https example

The prior example wasn't working for me.

Docker-DCO-1.1-Signed-off-by: Johannes 'fish' Ziemke <github@freigeist.org> (github: discordianfish)
Refactor client methods to stop code duplication

Docker-DCO-1.1-Signed-off-by: Johannes 'fish' Ziemke <github@freigeist.org> (github: discordianfish)
Add tls client auth, docs and tests

Docker-DCO-1.1-Signed-off-by: Johannes 'fish' Ziemke <github@freigeist.org> (github: discordianfish)