Support privleged app in APEX

privileged apps are installed to priv-app dir in APEX

Test: m
Change-Id: I8141e1c20e9486655606fa43b949783f11da09f4
diff --git a/apex/apex.go b/apex/apex.go
index 9382c19..96f4b5f 100644
--- a/apex/apex.go
+++ b/apex/apex.go
@@ -975,7 +975,11 @@
 }
 
 func getCopyManifestForAndroidApp(app *java.AndroidApp, pkgName string) (fileToCopy android.Path, dirInApex string) {
-	dirInApex = filepath.Join("app", pkgName)
+	appDir := "app"
+	if app.Privileged() {
+		appDir = "priv-app"
+	}
+	dirInApex = filepath.Join(appDir, pkgName)
 	fileToCopy = app.OutputFile()
 	return
 }