Open-source Bazel integration tests

It is a first batch of integration tests for Bazel. They tests some
basic behaviors and nominal cases of Bazel rules (especially they tests
the behavior of the examples provided in //examples).

--
MOS_MIGRATED_REVID=89440074
diff --git a/examples/py/BUILD b/examples/py/BUILD
index 6eecd4a..3963387 100644
--- a/examples/py/BUILD
+++ b/examples/py/BUILD
@@ -12,3 +12,8 @@
     srcs = ["bin.py"],
     deps = [":lib"],
 )
+
+filegroup(
+    name = "srcs",
+    srcs = ["BUILD"] + glob(["**/*.py"]),
+)