clientv3: close streams after use in lessor keepAliveOnce method
clientv3: close streams after use in lessor keepAliveOnce method

Streams are now closed after being used in the lessor `keepAliveOnce` method.
This prevents the "failed to receive lease keepalive request from gRPC stream"
message from being logged by the server after the context is cancelled by the
client.

Signed-off-by: Justin Kolberg <ddf45d6578c36b76a30bc5f620c283d41c59bd42@gmail.com>

etcd-io/etcd,etcd-io/etcd,ajityagaty/etcd,etcd-io/etcd,ajityagaty/etcd,ajityagaty/etcd