Support setting an empty object list in Configuration.

If an invocation is started with non-zero shard index and
if there is no IStrictShardableTest, it was failing with NPE
since Configuration.setTests() does not support setting an empty list.
This change is to fix the behavior.

BUG: 28554194
Change-Id: I102900ac485fd9508776c20d1d8c371bd3dd1eb0
2 files changed