fix(raft_server_stats.go) protect raft stats by a lock
fix(registry.go) protect the peer and proxy map in the registry by lock
fix(store.go) send event to watcher after we finish modifying it
fix(discovery_test.go) protect the garbageHandler by a lock
fix(internal_version_test.go) protect the checkedVersion by a lock
tests(test.sh) open race option
tests(snapshot_test) loose the timing assumption for snapshot test
Test run slowly on drone after open race option.
Merge pull request #710 from xiangli-cmu/fix_race

Fix race