Extract cacheFrom from original BuildImageConfiguration as a LIST instead of a STRING

See GH1455

Author: brenuart

src/main/java/io/fabric8/maven/docker/config/handler/property/PropertyConfigHandler.java

@@ -144,7 +144,7 @@ private BuildImageConfiguration extractBuildConfiguration(ImageConfiguration fro
                 .cleanup(valueProvider.getString(CLEANUP, config == null ? null : config.getCleanup()))
                 .noCache(valueProvider.getBoolean(NO_CACHE, config == null ? null : config.getNoCache()))
                 .squash(valueProvider.getBoolean(SQUASH, config == null ? null : config.getSquash()))
-                .cacheFrom(valueProvider.getString(CACHE_FROM, config == null ? null : (config.getCacheFrom() == null ? null : config.getCacheFrom().toString())))
+                .cacheFrom(valueProvider.getList(CACHE_FROM, config == null ? null : config.getCacheFrom()))
                 .optimise(valueProvider.getBoolean(OPTIMISE, config == null ? null : config.getOptimise()))
                 .entryPoint(extractArguments(valueProvider, ENTRYPOINT, config == null ? null : config.getEntryPoint()))
                 .assembly(extractAssembly(config == null ? null : config.getAssemblyConfiguration(), valueProvider))