Unlike Popen.communicate(), subprocess.call() doesn't read from the
stdout file descriptor. If the child process produces more output than
fits into the pipe buffer, it will block indefinitely.

If we don't intend to consume the output, just send it straight to
/dev/null to avoid this issue.
Signed-off-by: NSascha Silbe <silbe@linux.vnet.ibm.com>
Reviewed-by: NJanosch Frank <frankja@linux.vnet.ibm.com>
Message-Id: <1473192351-601-2-git-send-email-silbe@linux.vnet.ibm.com>
Signed-off-by: NFam Zheng <famz@redhat.com>