I regressed this in d4ced2ef77 ("allow plugins to have argument which match a
top-level flag.") by unconditionally overwriting any `PersistentRunE` that the
user may have supplied.
We need to ensure two things:
1. That the user can use `PersistentRunE` (or `PersistentRun`) for their own
purposes.
2. That our initialisation always runs, even if the user has used
`PersistentRun*`, since that will shadow the root.
To do this add a `PersistentRunE` to the helloworld plugin which logs (covers 1
above) and then use it when calling the `apiversion` subcommand (which covers 2
since that uses the client)
Signed-off-by: Ian Campbell <ijc@docker.com>
0b794e0620