Replace os.system with subprocess.call since the older function would
fail (more or less) silently if the executed program cannot be found
More info:
http://docs.python.org/library/subprocess.html#subprocess-replacements
[YOCTO #2454]
(From OE-Core rev: 57f843146ed62c04c23bc380dc8cb38aba264f1c)
Signed-off-by: Robert Yang <liezhi.yang@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>