Concurrent update test for etcd quota server (#777)
Concurrent update test for etcd quota server (#777)

* Concurrent update test for etcd quota server

* Review comments (tweak error messages / param names)

daviddrysdale/trillian,RJPercival/trillian,google/trillian,daviddrysdale/trillian,Martin2112/trillian,gdbelvin/trillian,daviddrysdale/trillian,AlCutter/trillian,Martin2112/trillian,codingllama/trillian,google/trillian,AlCutter/trillian,gdbelvin/trillian,RJPercival/trillian,codingllama/trillian,gdbelvin/trillian,Martin2112/trillian