sanity.bbclass: skip check_userns for non-local uid

sanity.bbclass: skip check_userns for non-local uid

Bitbake preserve network for non-local uid, refer [1],
so check_userns is not needed for non-local uid

[1] https://git.openembedded.org/bitbake/commit/?id=4eafae7904bae6e5c6bc50356e8a9077f2e207fa

Signed-off-by: Changqing Li <changqing.li@windriver.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit 808d0cece22bcbee15236717e158da247cbedaf1)
Signed-off-by: Steve Sakoman <steve@sakoman.com>