be explicit about app_id requirements in app_has_tasks
be explicit about app_id requirements in app_has_tasks

marathon appends leading slashes to our app ids - rather than
defensively testing for a leading slash before appending it, always
append to make it clear that the caller should *never* manage this
themselves

Yelp/paasta,gstarnberger/paasta,somic/paasta,Yelp/paasta,somic/paasta,gstarnberger/paasta