Upgrade bazlets to latest stable-2.15

Includes the following fixes:

- Bazel: Add fixes for --incompatible_load_python_rules_from_bzl
- Bazel: Export rules_python in plugin API
- Support bazelisk or bazel in tools/eclipse/project.py
- Rework imports in project.py
- Update project.py to use argparse
- Bazel: Add fixes for --incompatible_load_java_rules_from_bzl

Change-Id: If06e157079ef79120ef02b1023987d1f98451cf1

WORKSPACE

diff --git a/WORKSPACE b/WORKSPACE
index f4e21cf..430444d 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -3,7 +3,7 @@
 load("//:bazlets.bzl", "load_bazlets")
 
 load_bazlets(
-    commit = "4b3ce19d8d18d9f7df56a06532723b91ea6949d0",
+    commit = "1aa9482d30e8873e6d3e1e75dc307a43aae0482e",
     #local_path = "/home/<user>/projects/bazlets",
 )