Ruby: Connect system port in Ruby network test

This patch moves the connection of the system port to create_system in
Ruby.py. Thereby it allows the failing Ruby test (and other Ruby
systems) to run again.

tests/configs/simple-atomic-mp-ruby.py

@@ -47,6 +47,8 @@ for cpu in cpus:
 # connect memory to membus
 system.physmem.port = system.membus.port
 
+# Connect the system port for loading of binaries etc
+system.system_port = system.membus.port
 
 # -----------------------
 # run simulation