slaprunner: uses sshkeys_authority recipe to manage openssh keys, otherwise they may change at any slapos run

This makes easier the development of the webrunner, as it can be deployed within a webrunner

Changes include:
  * new parameter "no-ipv4-frontend" to prevent the request of an ipv4 frontend. The webrunner cannot provide one, so let's get rid of failing promises.
  * new paramaters to define the ports of the ssh servers (for runner-importer and runner-exporter). Then no colliding when servers run on the same IP.

In case of erp5testnode, we have only one IP. So slapos node instance on clone instance would reach... slapproxy of main slaprunner.

Let the supervisord of slaprunner managing the instance processes
be managed by supervisord of slapos node.

Fixes problems of process like supervisord escaping control.

Also remove unused variable in nginx-conf.

+ make promise checking this

  Missing update on parts, slapos-repo needs to be explicitly invoked.

Supervisord will replace Popen instructions

Conflicts:
	software/slaprunner/instance-runner.cfg