Enable BuildBucket plugin for LUCI

https://g3doc.corp.google.com/third_party/java_src/gerritcodereview/plugins/buildbucket/README.md?cl=513247393

Change-Id: Ie3af413638113f835e4fcc95deacd02f7efb6057
Reviewed-on: https://go-review.googlesource.com/c/All-Projects/+/472575
Reviewed-by: Heschi Kreinick <heschi@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>

buildbucket.config

diff --git a/buildbucket.config b/buildbucket.config
new file mode 100644
index 0000000..0af87d8
--- /dev/null
+++ b/buildbucket.config
@@ -0,0 +1,5 @@
+[host]
+	git = "go.googlesource.com"
+	gerrit = "go-review.googlesource.com"
+
+[bucket "luci.golang.try"]