Fix KeySplitRouteTest.TestReplicaCounts
Fix KeySplitRouteTest.TestReplicaCounts

Summary:
Fix KeySplitRouteTest.TestReplicaCounts

There is a known issue with using ASSERT_DEATH() in TSAN mode. So, skipping the part with ASSERT_DEATH() when the mode is TSAN mode.

Reviewed By: djvaporize

Differential Revision: D26618433

fbshipit-source-id: 7aa8393615c177edc5d641bae1f2b3381dc4688b

facebook/mcrouter,facebook/mcrouter,facebook/mcrouter,facebook/mcrouter