Deal with container shutdown race condition.
Deal with container shutdown race condition.

Newer versions of Docker appear to produce a NullResource exception instead of
an APIError when a container is referenced after it's been shut down, so check
for this as well.

Change-Id: I2f478637e54acddd01f70564f8ccba11bdfcaf08

GoogleCloudPlatform/appstart,GoogleCloudPlatform/appstart