The source of problem was the fact that multiple tests were creating
their clusters (and some of them were setting global grpclog).
If the test was running after some other test that created HttpServer
(so accessed grpclog), this was reported as race.
Tested with:
go test ./clientv3/. -v "--run=(Example).*" --count=2
go test ./clientv3/. -v "--run=(Test).*" --count=2
go test ./integration/embed/. -v "--run=(Test).*" --count=2
