Remove Slave role

Removing the Jenkins slave reduces our set of images to two: the install
server and the SF role itself. The Jenkins slave is basically just an
additional Jenkins plugin, all other dependencies are already covered by
the SF role itself.

This patch also add a startup systemd definition for the
swarm client.

Change-Id: I931d61aa8c2fc676d6eec8cab79cf15f60483c3f
Merge "Remove Slave role"