vaultutil: add disable_clustering=true
vaultutil: add disable_clustering=true

Otherwise it will keep printing the error:

```
grpc: addrConn.resetTransport failed to create client transport:
connection error: desc = "transport: Error while dialing dial tcp
10.3.141.62:8201: getsockopt: connection timed out"; Reconnecting to
{example-vault.e2e-local:8201 <nil>}
```

coreos/vault-operator,coreos/vault-operator