According to Darren's suggestion, subprocess.call() will wait until the
subprocess complete. So simplify the code, use subprocess.call() to wait
command complete.
(Bitbake rev: 3dea9d5a5af82d99d337238981807a4cb1bd5b93)
Signed-off-by: Kang Kai <kai.kang@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>