specifying a custom dockerfile in configuration.dockerfile doesn't work for flex deployment

[patflynn]

https://github.com/patflynn/kplay/blob/master/spring-boot-basic/pom.xml#L112

It looks like configuration.dockerfile is only for standard and is being ignored and my src/main/docker directory is being included instead. This is unexpected as the dockerfile property is scoped to the whole plugin. I'd also like to be able to either specify a dockerfile location, or a docker directory location for both flex and standard deployments.