This fix tries to address the inconsistency in #22036 where labels
set on the command line will not override labels specified in
Dockerfile, but will override labels inherited from `FROM` images.
The fix add a LABEL with command line options at the end of the
processed Dockerfile so that command line options labels always
override the LABEL in Dockerfiles (or through `FROM`).
An integration test has been added for test cases specified in #22036.
This fix fixes#22036.
NOTE: Some changes are from #22266 (@tiborvass).
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>
Upstream-commit: 5844736c14b29860ea03b040e9a052e59ad75bfc
Component: engine
