Add Dockerfile for special file permission test

integration/dockerfiles/Dockerfile_test_cache_perm

@@ -0,0 +1,10 @@
+# Test to make sure the cache works with special file permissions properly.
+# If the image is built twice, directory foo should have the sticky bit,
+# and file bar should have the setuid and setgid bits.
+
+FROM alpine as base_stage
+
+FROM ubuntu:16.04
+
+RUN mkdir foo && chmod +t foo
+RUN touch bar && chmod u+s,g+s bar

integration/images.go

@@ -134,6 +134,7 @@ func NewDockerFileBuilder(dockerfiles []string) *DockerFileBuilder {
 	d.TestCacheDockerfiles = map[string]struct{}{
 		"Dockerfile_test_cache":         {},
 		"Dockerfile_test_cache_install": {},
+		"Dockerfile_test_cache_perm":    {},
 	}
 	return &d
 }