Execute command in a subshell, return stdout.

    Stderr is unbuffered from the subshell.x

def sh2(cmd):
    """Execute command in a subshell, return stdout.

    Stderr is unbuffered from the subshell.x"""
    p = Popen(cmd, stdout=PIPE, shell=True, env=sub_environment())
    out = p.communicate()[0]
    retcode = p.returncode
    if retcode:
        raise CalledProcessError(retcode, cmd)
    else:
        return out.rstrip()