All tests passing for TRN-328

Ticket content:

We currently use https://godoc.org/github.com/dropbox/godropbox/container/lrucache for caching in our datastore and dnscache, but it turns out this is not thread-safe and is crashing when running with GOMAXPROCS>1 in productions.

We should swap it out with http://godoc.org/github.com/hashicorp/golang-lru