For ENG-5489, remove locking from StatsAgent that causes deadlocks registering stats at startup
For ENG-5489, dummy mode works a lot better if it's turned on /facepalm
Revert "For ENG-5489, dummy mode works a lot better if it's turned on /facepalm"

This reverts commit 7e4f064a6f4ceec1a2ed590f90dbec759ac93d64.
For ENG-5489, add explanation of putIfAbsent idiom
Merge pull request #941 from VoltDB/ENG-5489

For ENG-5489, remove locking from StatsAgent that causes deadlocks regis...