Add some more details to doc on devstack via heat
Add some more details to doc on devstack via heat

Make it more explicit how to use the key pair and how to see
what happened with devstack.

SUSE-Cloud/automation,aspiers/automation,aspiers/automation,aspiers/automation,gosipyan/automation,aspiers/automation,SUSE-Cloud/automation,gosipyan/automation,gosipyan/automation,SUSE-Cloud/automation,SUSE-Cloud/automation,gosipyan/automation