This fix tries to address the issue raised on 29185 where
`docker inspect <unknown object>` on Windows will return:
```
Error response from daemon: plugins are not supported on this platform
```
The reason was that in case `--type` is not specified, `docker inspect`
will iterate through different types `container`, `image`, `network`,
`plugin` etc. The `plugin` object is the last type to check.
However, as `plugin` is not supported on Windows yet, the error message
is not very informative for `plugins are not supported on this platform`.
This fix tries to fix the issue by return a `not found` error on unsupported
platforms as well.
An integration test has been added to cover the changes for Windows/Linux.
This fix fixes 29185.
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>
Yong Tang