Make nat test less racy and accurate

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>
Merge pull request #7832 from crosbymichael/fix-nat-test

Make nat test less racy and accurate
Add more error info to TestDockerRunEchoStdoutWithMemoryLimit

This test fails on my CI server often so we need more info when it does
happen with this test.

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>
Merge pull request #7833 from crosbymichael/mem-test

Add more error info to TestDockerRunEchoStdoutWithMemoryLimit