Add Bazel itself in downstream project (#434)

This will help prevent https://github.com/bazelbuild/bazel/issues/7026
diff --git a/buildkite/bazelci.py b/buildkite/bazelci.py
index 1fa4d52..dca23d8 100644
--- a/buildkite/bazelci.py
+++ b/buildkite/bazelci.py
@@ -49,6 +49,11 @@
         "http_config": "https://raw.githubusercontent.com/googlesamples/android-testing/master/bazelci/buildkite-pipeline.yml",
         "pipeline_slug": "android-testing"
     },
+    "Bazel": {
+        "git_repository": "https://github.com/bazelbuild/bazel.git",
+        "http_config": "https://raw.githubusercontent.com/bazelbuild/bazel/master/.bazelci/postsubmit.yml",
+        "pipeline_slug": "bazel"
+    },
     "Bazel Remote Execution": {
         "git_repository": "https://github.com/bazelbuild/bazel.git",
         "http_config": "https://raw.githubusercontent.com/bazelbuild/continuous-integration/master/buildkite/pipelines/bazel-remote-execution-postsubmit.yml",