Port the main php_cli_server.inc to use ephemeral ports, thus
allowing CLI server tests to be parallelized.
A complication here is that we also need to give each test a
separate doc root, to avoid index.php files writing over each
other.
Closes GH-6375.
In practice, we always act as an HTTP/1.1 client, for compatibility
with servers which ignore protocol version. Sending the version in
the request will avoid problems with servers which don't ignore it.
HTTP/1.0 can still be forced using a stream context option.
Closes GH-5899.
