Mark //src/test/java/com/google/devtools/build/lib:shell_test as flaky.

Issue #248

--
MOS_MIGRATED_REVID=113990796
diff --git a/src/test/java/com/google/devtools/build/lib/BUILD b/src/test/java/com/google/devtools/build/lib/BUILD
index e6b6b93..446705b 100644
--- a/src/test/java/com/google/devtools/build/lib/BUILD
+++ b/src/test/java/com/google/devtools/build/lib/BUILD
@@ -660,6 +660,7 @@
     data = [
         ":shell/killmyself",
     ],
+    flaky = True,
     tags = ["shell"],
     test_class = "com.google.devtools.build.lib.AllTests",
     deps = [