We were previously using the sandbox process's stdio as the root container's
stdio. This makes it difficult/impossible to distinguish output application
output from sandbox output, such as panics, which are always written to stderr.
Also close the console socket when we are done with it.
PiperOrigin-RevId: 215585180
Change-Id: I980b8c69bd61a8b8e0a496fd7bc90a06446764e0