Execute command in a subshell, return stdout, stderr

    If anything appears in stderr, print it out to sys.stderr

def sh3(cmd):
    """Execute command in a subshell, return stdout, stderr

    If anything appears in stderr, print it out to sys.stderr"""
    p = Popen(cmd, stdout=PIPE, stderr=PIPE, shell=True,
              env=sub_environment())
    out, err = p.communicate()
    retcode = p.returncode
    if retcode:
        raise CalledProcessError(retcode, cmd)
    else:
        return out.rstrip(), err.rstrip()