Fix tf.matching_files issue with access denied subdirectory.

This fix tries to address the issue raised in 19274 where
tf.matching_files will return an error if no permission for
subdirectories (Even if the subdirectories does not match).

This fix addresses the issue by ignore the case for `permisson denied`
during the directory traversal.

This fix fixes 19274.

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>