This fix tries to address the issue raised in #23528 where
docker labels caused journald log error because journald
has special requirements on field names.
This fix addresses this issue by sanitize the labels per
requirements of journald.
Additional unit tests have been added to cover the changes.
This fix fixes#23528.
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>
Yong Tang