tests/integration: Move of naming/snapshot clientv3 tests (and yaml reference)

path change in clientv3/yaml/config_test

git mv clientv3/naming/grpc_test.go         tests/integration/clientv3/grpc_test.go
git mv clientv3/snapshot/*_test.go          tests/integration/snapshot
git mv clientv3/{main_test.go,example_*.go} tests/integration/clientv3/examples/