If the CNI network plugin completes successfully, but something fails
between that success and dockerhsim's sandbox setup code, plugin resources
may not be cleaned up. A non-trivial amount of code runs after the
plugin itself exits and the CNI driver's SetUpPod() returns, and any error
condition recognized by that code would cause this leakage.

The Kubernetes CRI RunPodSandbox() request does not attempt to clean
up on errors, since it cannot know how much (if any) networking
was actually set up. It depends on the CRI implementation to do
that cleanup for it.

In the dockershim case, a SetUpPod() failure means networkReady is
FALSE for the sandbox, and TearDownPod() will not be called later by
garbage collection even though networking was configured, because
dockershim can't know how far SetUpPod() got.

Concrete examples include if the sandbox's container is somehow
removed during during that time, or another OS error is encountered,
or the plugin returns a malformed result to the CNI driver.

Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1532965