dag_tools: get_children and get_parents should respect valid_if_or

[adgaudio]

if valid_if_or is set on an application, then get_children should by default only show children where the child job_id passes the valid_if_or criteria.

{
"app1": {"job_id_template": "{client_id}"}, ...},

"app2": {"valid_if_or": {"client_id": [1,2,3]},
              "job_id_template": "{client_id}",
              "depends_on": {"app_name": ["app1"], ...}
}

dag_tools.get_children("app1", "4")  # --> should return []
dag_tools.get_children("app1", 3)  # --> should return ("app2", 3)