Fix the following error in integration pipeline,
```
=== RUN TestTLSReloadCopy
v3_grpc_test.go:1754: tls: failed to find any PEM data in key input
v3_grpc_test.go:1754: tls: private key does not match public key
v3_grpc_test.go:1754: tls: private key does not match public key
v3_grpc_test.go:1754: tls: private key does not match public key
```
Refer to https://github.com/etcd-io/etcd/runs/7123775361?check_suite_focus=true
Signed-off-by: Benjamin Wang <wachao@vmware.com>