When doing remote execution, it was sometimes failing with the following
exception: OSError: [Errno 10] No child processes.
The problem is when using libev default loop, the latest register a handler for
SIGCHLD, it causes a problem when Popen.communicate() tried to do a wait_pid,
the syscall is skipped because of the signal. Then when wait_pid is called
again, it failed because the process don't exist anymore.