spring-boot:build-image has a layout parameter that cannot be always be honoured

[wilkinsona]

The layout and perhaps also the layoutFactory parameters on spring-boot:build-image don't make complete sense. For example, image building is currently limited to jar files yet the layout can be set to war. The parameters are also listed as being since 1.0 and 1.5 respectively, but image building was a new feature in 2.3. Perhaps BuildImageMojo shouldn't extend AbstractPackagerMojo?

[philwebb]

We'll move both out of AbstractPackagerMojo and push them to the subclass.