Bazel: Switch to using bazlets

We prefer to consume maven_jar custom rule from bazlets repository, for
the same reasons as in Gerrit project:

* caching atifacts across different clones and projects
* exposing source classifiers and neverlink artifact

Change-Id: Ia560a68136186025926649f6985608fcf326082f

tools/BUILD

diff --git a/tools/BUILD b/tools/BUILD
new file mode 100644
index 0000000..8b13789
--- /dev/null
+++ b/tools/BUILD
@@ -0,0 +1 @@
+

tools/bazlets.bzl

diff --git a/tools/bazlets.bzl b/tools/bazlets.bzl
new file mode 100644
index 0000000..e14e488
--- /dev/null
+++ b/tools/bazlets.bzl
@@ -0,0 +1,17 @@
+NAME = "com_googlesource_gerrit_bazlets"
+
+def load_bazlets(
+    commit,
+    local_path = None
+  ):
+  if not local_path:
+      native.git_repository(
+          name = NAME,
+          remote = "https://gerrit.googlesource.com/bazlets",
+          commit = commit,
+      )
+  else:
+      native.local_repository(
+          name = NAME,
+          path = local_path,
+      )