Intermittently the read_pref_multi_mongos_stale_config.js test fails across different 2.7 builds.
https://mci.10gen.com/task/mongodb_mongo_master_linux_64_debug_716cfde34adf0e1c4a92c4e8fc1960a50d3cbc50_14_11_07_15_40_07_sharding_linux_64_debug