Host can log a grpc ConnectionAbortedException during normal shutdown

[brettsam]

During a normal shutdown, the worker process may exit before the grpc connection has been gracefully terminated. We need to fix the ordering here so this doesn't happen. It causes noisy (and worrying) exceptions to be logged, when really this is just normal behavior, and the host is shutting down anyway.

The exception that can be seen is:

System.IO.IOException : The request stream was aborted. ---> Microsoft.AspNetCore.Connections.ConnectionAbortedException : The HTTP/2 connection faulted. ---> Microsoft.AspNetCore.Connections.ConnectionResetException : An existing connection was forcibly closed by the remote host. ---> System.Net.Sockets.SocketException : An existing connection was forcibly closed by the remote host.
   at Microsoft.AspNetCore.Server.Kestrel.Transport.Sockets.Internal.SocketAwaitableEventArgs.<GetResult>g__ThrowSocketException|5_0(SocketError e)
 ...snip...
   at async Grpc.AspNetCore.Server.Internal.HttpContextStreamReader`1.<MoveNext>g__MoveNextAsync|9_0[TRequest](??)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at async Microsoft.Azure.WebJobs.Script.Grpc.FunctionRpcService.EventStream(IAsyncStreamReader`1 requestStream,IServerStreamWriter`1 responseStream,ServerCallContext context) at /_/src/WebJobs.Script.Grpc/Server/FunctionRpcService.cs : 73