A static global initialiser happens before the arguments are parsed, so we need
to calculate the path later.
Signed-off-by: Ian Campbell <ijc@docker.com>
To do this we add a stub `cobra.Command` for each installed plugin (only when
invoking `help`, not for normal running).
This requires a function to list all available plugins so that is added here.
Signed-off-by: Ian Campbell <ijc@docker.com>
Also includes the scaffolding for finding a validating plugin candidates.
Argument validation is moved to RunE to support this, so `noArgs` is removed.
Signed-off-by: Ian Campbell <ijc@docker.com>
