Failure on MCI:

https://mci.10gen.com/ui/task/mongodb_mongo_master_linux_64_c9b019d326dca25c7f88abb5b74aef2476b69aec_13_08_15_03_45_06_sharding_linux_64

Same run passed on buildbot:

http://buildlogs.mongodb.org/Linux%2064-bit/builds/5724/test/sharding/shard_kill_and_pooling.js

Talked to Greg, he thinks it may be related to timing and the sharding test itself.