fixed playbook path in startup script

The code was looking for playbooks inside `/opt/slapos.playbook/playbooks`, but in fact the playbooks are at `/opt/slapos.playbook/`

playbook/roles/standalone-shared/templates/start-script.j2

 #!/bin/bash
 # Reruns the ansible playbook, does nothing else
 
-cd /opt/slapos.playbook/playbook/
+cd /opt/slapos.playbook/
 
 ansible-playbook {{ startup_playbook_id }}  -i  hosts --connection=local