[#67794884] Removing possible race condition when mulitple apps get staged at the same time

Signed-off-by: Johannes Tuchscherer <jtuchscherer@pivotallabs.com>
Before listening to a new instance, make sure that is has a warden job id and a warden container path

Signed-off-by: Johannes Tuchscherer <jtuchscherer@pivotallabs.com>