TLS support for docker endpoint

[kasra73]

What's the problem?

In order to prevent apps and other containers from unwanted access to docker endpoint, we can configure self-signed SSL for docker daemon. Tsuru support this feature in tsuru node-add command using cert flags. but this causes a connection problem when big-sibling try to get logs and containers info from the endpoint. After some digging we can find out docker.NewClient is not the function to be used for tls connection and docker.NewTLSClient should be used instead:
docker.NewTLSClient(endpoint, cert, key, ca)
reference: https://github.com/fsouza/go-dockerclient#using-with-tls

How to fix it?

I changed config to get tls support parameters in addition to docker endpoint. So the struct DockerConfig has been created for this purpose. Then we can use a volume for cert, key and ca files which will be available in /docker-certs path inside the container. If files doesn't exists, bs will simply ignore tls support.

How to use this feature?

First your node address must begin with https: and of course it will if you want to use tls connection. Then you should update bs service by tsuru command and attach cert files directory to your bs container as a volume:
tsuru node-container-update big-sibling -v /home/user/.docker:/docker-certs -v /proc:/prochost
Note that /proc:/prochost is required because using -v command will override volume config.