The error is not global since we don't use "from os import *", so it
should be os.error.

[YOCTO #4489]

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

Update older code to use modern exception handling syntax which
is the form accepted by python 3.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

Currently, various standard library operations like os.walk(),
os.path.isdir() and os.path.islink() each call stat or lstat which
involves a syscall into the kernel. There is no caching since they could
conceivably have changed on disk. The result is that for something like
the do_package task of the kernel we're spending over two minutes making
868,000 individual stat calls for 23,000 files. This is suboptimal.

This patch adds lib/oe/cachedpath.py which are a set of replacement
functions for these operations which use cached stat data rather than
hitting the kernel each time. It gives a nice performance improvement
halving the build time of the kernel do_package.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>