BuildEnv: Eliminate RUBY as build environment variable
This patch replaces RUBY with PROTOCOL in all the SConscript files as
the environment variable that decides whether or not certain components
of the simulator are compiled.

scons: rename TraceFlags to DebugFlags

testers: move testers to a new directory

This patch moves the testers to a new subdirectory under src/cpu and includes
the necessary fixes to work with latest m5 initialization patches.