Test that a disconnect after the write request but before the data is an error

tests/acceptance/fakes/dest/close_after_hello.rb

@@ -9,7 +9,8 @@
 require 'flexnbd/fake_dest'
 include FlexNBD
 
-server = FakeDest.new( *ARGV )
+addr, port = *ARGV
+server = FakeDest.new( addr, port )
 client = server.accept( "Timed out waiting for a connection" )
 client.write_hello
 client.close