Log base image@digest when building (ko-build#592)

* Log base image@digest when building

* Only log full digest if the original base wasn't already specified by digest

* Remove redundant image ref

pkg/commands/config.go

@@ -106,12 +106,21 @@ func getBaseImage(bo *options.BuildOptions) build.GetBase {
 			return ref, cached, nil
 		}
 
-		log.Printf("Using base %s for %s", ref, s)
 		result, err := fetch(ctx, ref)
 		if err != nil {
 			return ref, result, err
 		}
 
+		if _, ok := ref.(name.Digest); ok {
+			log.Printf("Using base %s for %s", ref, s)
+		} else {
+			dig, err := result.Digest()
+			if err != nil {
+				return ref, result, err
+			}
+			log.Printf("Using base %s@%s for %s", ref, dig, s)
+		}
+
 		cache[ref.String()] = result
 		return ref, result, nil
 	}