Send error message to docker/kubectl exec on failure

Containerd uses the last error message sent to the log to
print as failure cause for create/exec. This required a
few changes in the logging logic for runsc:
  - cmd.Errorf/Fatalf: now writes a message with 'error'
    level to containerd log, in addition to stderr and
    debug logs, like before.
  - log.Infof/Warningf/Fatalf: are not sent to containerd
    log anymore. They are mostly used for debugging and not
    useful to containerd. In most cases, --debug-log is
    enabled and this avoids the logs messages from being
    duplicated.
  - stderr is not used as default log destination anymore.
    Some commands assume stdio is for the container/process
    running inside the sandbox and it's better to never use
    it for logging. By default, logs are supressed now.

PiperOrigin-RevId: 251881815

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