This fix is a follow up for comment:
https://github.com/docker/docker/pull/29186/files#r91277345
While #29186 addresses the issue of `docker inspect <unknown object>`
on Windows, it actually makes `docker plugin inspect <unknown object>`
out `object not found` on Windows as well. This is actually misleading
as plugin is not supported on Windows.
This fix reverted the change in #29186 while at the same time,
checks `not supported` in `docker inspect <unknown object>` so that
- `docker plugin inspect <unknown object>` returns `not supported` on Windows
- `docker inspect <unknown object>` returns `not found` on Windows
This fix is related to #29186 and #29185.
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>