explicitly fail if no images are found when running remote tests

The previous implementation succeeds if no images are run. This causes
silent failures when image matchers are provided that do not match any image.

Author: MHBauer

test/e2e_node/runner/remote/run_remote.go

@@ -244,6 +244,10 @@ func main() {
 					klog.Fatalf("Could not retrieve list of images based on image prefix %q and family %q: %v",
 						imageConfig.ImageRegex, imageConfig.ImageFamily, err)
 				}
+				if len(images) == 0 { // if we have no images we can't run anything
+					klog.Fatalf("No matching images retrieved on image prefix %q and family %q: %v",
+						imageConfig.ImageRegex, imageConfig.ImageFamily, err)
+				}
 			} else {
 				images = []string{imageConfig.Image}
 			}