config: move ruby objects under ruby_system in obj hierarchy

config: move ruby objects under ruby_system in obj hierarchy
This patch moves the contollers to be children of the ruby_system instead of
'system' under the python object hierarchy. This is so that these objects
can inherit some of the ruby_system's parameter values without resorting to
calling a global system pointer during run-time.

Committed by: Nilay Vaish <nilay@cs.wisc.edu>