"Playbook not found for project" error when the playbook exist but is invalid

ISSUE TYPE

When a playbook is not valid but its filename is specified using a rest api enpoint, (e.g using job_templates endpoint) the system returns "Playbook not found for project".

SUMMARY

Error "Playbook not found for project", suggest users that yaml file doesn't exist at specified playbook path. In this particular situation error message like "Playbook specified doesn't contain any plays" or "Playbook specified is not a valid playbook" would clearly suggest user where problem lies.