Update bazlets to latest revision on stable-2.15

- Add optional dir_name argument to gerrit_plugin
- gerrit_plugin: Improve stamping error message
- Upgrade Gerrit API to version 2.15.2
- Set Gerrit API snapshot version to 2.15.2-SNAPSHOT
- Fix the error in project properties generation file
- Switch to 2.14.9-SNAPSHOT Gerrit API version for local dev
- Fix deletion of Sonar Scanner folder
- Automate SonarQube analysis for plugins built with bazel

Change-Id: I8928a5db8dcbfc6978f9b500efe4d633ea763c73
diff --git a/WORKSPACE b/WORKSPACE
index f8451b4..1126cdc 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -3,7 +3,7 @@
 load("//:bazlets.bzl", "load_bazlets")
 
 load_bazlets(
-    commit = "df6622a4e725b4d0bad99377f05749171a8c94b9",
+    commit = "ad9df4d323c1df5c733d379c8891bde13a00a285",
     #    local_path = "/home/<user>/projects/bazlets",
 )