Persistent volume caching for base images (#383)

* comments

* initial commit for persisent volume caching

* cache warmer works

* general cleanup

* adding some debugging

* adding missing files

* Fixing up cache retrieval and cleanup

* fix tests

* removing auth since we only cache public images

* simplifying the caching logic

* fixing logic

* adding volume cache to integration tests. remove auth from cache warmer image.

* add building warmer to integration-test

* move sample yaml files to examples dir

* small test fix

pkg/executor/build.go

@@ -54,7 +54,7 @@ type stageBuilder struct {
 
 // newStageBuilder returns a new type stageBuilder which contains all the information required to build the stage
 func newStageBuilder(opts *config.KanikoOptions, stage config.KanikoStage) (*stageBuilder, error) {
-	sourceImage, err := util.RetrieveSourceImage(stage, opts.BuildArgs)
+	sourceImage, err := util.RetrieveSourceImage(stage, opts.BuildArgs, opts)
 	if err != nil {
 		return nil, err
 	}