They were listed twice in `docker --help` (but not `docker help`), since the
stubs were added in both `tryRunPluginHelp` and the `setHelpFunc` closure.
Calling `AddPluginStubCommands` earlier in `setHelpFunc` before the call to
`tryRunPluginHelp` is sufficient. Also it is no longer necessary to add just
valid plugins (`tryRunPluginHelp` handles invalid plugins correctly) so remove
that logic (which was in any case broken for e.g. `docker --help`).
Update the e2e test to check for duplicate entries and also to test `docker
--help` which was previously missed.
Signed-off-by: Ian Campbell <ijc@docker.com>
baabf6e8ad