Add a umask context manager which can be used to temporarily change the
umask in a 'with' block.
(Bitbake rev: 6c601e68a27e1c60b04c2a61830d1812cc883e09)
Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>