The code now ensures that each of the test is running in its own directory as opposed to shared os.tempdir.
```
$ (cd tests && env go test -timeout=15m --race go.etcd.io/etcd/tests/v3/integration/clientv3/examples -run ExampleAuth)
2022/04/03 10:24:59 Running tests (examples): ...
2022/04/03 10:24:59 the function can be called only in the test context. Was integration.BeforeTest() called ?
2022/04/03 10:24:59 2022-04-03T10:24:59.462+0200 INFO m0 LISTEN GRPC {"member": "m0", "grpcAddr": "localhost:m0", "m.Name": "m0"}
```
% (cd tests && go vet ./...)
stderr: # go.etcd.io/etcd/tests/v3/integration/clientv3/concurrency_test
stderr: integration/clientv3/concurrency/election_test.go:74:6: call to (*T).Fatal from a non-test goroutine
stderr: integration/clientv3/concurrency/mutex_test.go:57:4: call to (*T).Fatal from a non-test goroutine
They used to take >10min with coverage, so were causing interrupted
Travis runs.
Know thay fit in 100-150s (together), thanks also to parallel
execution.
