Use the dockerenv file from the current dir instead of root

Docker-DCO-1.1-Signed-off-by: Guillaume J. Charmes <guillaume.charmes@docker.com> (github: creack)
Upstream-commit: e84e344b1f887f06852953bc75912fc24a64d08a
Component: engine

components/engine/sysinit/sysinit.go

@@ -66,7 +66,7 @@ func SysInit() {
 
 	// Get env
 	var env []string
-	content, err := ioutil.ReadFile("/.dockerenv")
+	content, err := ioutil.ReadFile(".dockerenv")
 	if err != nil {
 		log.Fatalf("Unable to load environment variables: %v", err)
 	}