test: Wait for job down events in TestDeployController
test: Wait for job down events in TestDeployController

Getting a deployment complete event no longer guarantees that all the
old jobs have been scaled down (see #3395), so we need to wait for them
explicitly.

Signed-off-by: Lewis Marshall <748e1641a368164906d4a0c0e3965345453dcc93@lmars.net>

lmars/flynn,lmars/flynn,philiplb/flynn,flynn/flynn,philiplb/flynn,lmars/flynn,philiplb/flynn,lmars/flynn,lmars/flynn,flynn/flynn,philiplb/flynn,philiplb/flynn,flynn/flynn,flynn/flynn,flynn/flynn