Add OpenSuse support

- Add Opensuse to the OS list and add required commands
Add SLES to the list since this is the same as OpenSuse
Make the end cmd configurable

This allows us to set an other command then the default /usr/sbin/sshd -D
Increase read/write timeouts to docker

This change increases the read and write timeouts to the docker api.
By default this is 60 seconds
Install ssh client stuff as well. otherwise scp commands will fail.
Update readme and minor modifications

Update readme with new functionality
Modified read/write timeout configuration
Renamed docker_entrypoint to docker_cmd to avoid confusion with the docker entrypoint config option
Added extra ssh options for OpenSuSE/SLES