Clean up stager test

Signed-off-by: Max Brunsfeld <mbrunsfeld@pivotallabs.com>
Stop using nats queues

Every stager can try to create a task for every diego.staging.start
message. Only one will succeed

Signed-off-by: Max Brunsfeld <mbrunsfeld@pivotallabs.com>
Update deps

Signed-off-by: Max Brunsfeld <mbrunsfeld@pivotallabs.com>