Add support for using different docker images

The part of trying out scripts involve creating a docker container with
ssh and running some projects and functions on it.

This change allows to define the docker image name to be used with the
docker-* functions.

lib/kickstart-docker-ssh

@@ -1,6 +1,9 @@
 #!/bin/bash -e
 
-runnig_sshd=$(docker ps -q moul/sshd)
+image_name=${1:-$KICKSTART_DOCKER_IMAGE}
+image_name=${image_name:-moul/sshd}
+
+runnig_sshd=$(docker ps -q $image_name)
 [ -z "$runnig_sshd" ] && echo "Docker container not created. Run \`kickstart docker-create\` to get one" && exit 1
 
 port=`docker port $runnig_sshd 22 | cut -f 2 -d :`