This regressed in 3af168c7df ("Ensure plugins can use `PersistentPreRunE`
again.") but this wasn't noticed because the helloworld test plugin has it's
own `PersistentPreRunE` which has the effect of deferring the resolution of the
global variable. In the case where the hook isn't used the variable is resolved
during `newPluginCommand` which is before the global variable was set.
Initialize the plugin command with a stub function wrapping the call to the
(global) hook, this defers resolving the variable until after it has been set,
otherwise the initial value (`nil`) is used in the struct.
Signed-off-by: Ian Campbell <ijc@docker.com>
Ian Campbell