No EOS sent for ServerReflectionInfo request

While working with grpcurl with some HTTP/2 proxies between `grpcurl` and the gRPC server, I noticed that for the following request:
```
$ grpcurl -v -plaintext -d '{"name": "Laurent"}' localhost:8080 helloworld.Greeter/SayHello
```
`grpcurl` actually sends 2 requests:
- a first one to `/grpc.reflection.v1alpha.ServerReflection/ServerReflectionInfo` (to get the proto definition if I'm right)
- a second one which is the actual call to the requested service `/helloworld.Greeter/SayHello`

But I noticed that the first request does not send the EOS (End Of Stream) flag .
So if the proxy in between, instead of streaming directly the incoming request, buffers the request (for whatever reason), it waits indefinitely for the EOS flag.

Based on the following document https://github.com/grpc/grpc/blob/master/doc/PROTOCOL-HTTP2.md I think the DATA frame of the `ServerReflectionInfo` request should be flagged with `END_STREAM`.

Start by reproducing the grpcurl command with an HTTP/2 proxy that buffers requests, then trace the ServerReflectionInfo request and its DATA framing. Done means the reflection request sends END_STREAM so the proxy does not wait indefinitely before forwarding it.

Written by the indexing model from the issue text.