Increase the shard count of //src/test/shell/bazel:bazel_test_test

This test has some occasional timeout flakes.

See http://ci.bazel.io/job/bazel-tests/BAZEL_VERSION=latest,PLATFORM_NAME=darwin-x86_64/148/console

--
MOS_MIGRATED_REVID=128684898

src/test/shell/bazel/BUILD

diff --git a/src/test/shell/bazel/BUILD b/src/test/shell/bazel/BUILD
index 443e010..b326145 100644
--- a/src/test/shell/bazel/BUILD
+++ b/src/test/shell/bazel/BUILD
@@ -129,6 +129,7 @@
     name = "bazel_test_test",
     srcs = ["bazel_test_test.sh"],
     data = [":test-deps"],
+    shard_count = 3,
 )
 
 sh_test(