Issue Template

Title: HTTP/1.0 responses without Connection: keep-alive should be closed.

Description:
The HTTP/1.0 specification says that connections carry a single request and then are closed unless the response includes "Connection: keep-alive".

[optional Relevant Links:]
https://tools.ietf.org/html/rfc1945
https://en.wikipedia.org/wiki/HTTP_persistent_connection

Bug Template

Title: HTTP/1.0 connections with no Connection header are kept alive when they should be closed.

Description:
HTTP/1.0 connections with no Connection header are kept alive when they should be closed. This can cause 503 errors if the connection is reused.

Repro steps:
Set up envoy in front of a flask server (which is HTTP/1.0) and run siege against it. You will see Failed transactions.