runsc: Fix flakey container_test.
runsc: Fix flakey container_test.

Verified that this is no longer flakey over 10K repetitions.

PiperOrigin-RevId: 201267499
Change-Id: I793c916fe725412aec25953f764cb4f52c9fbed3

google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor