drcachesim: add offline trace file support

Split from #1703 (closed)

The drcachesim design isolates the source of memory references, allowing us to add an offline trace file feature to complement the live, online default operation. This issue covers adding both tracer output to a file and simulator input from a file.

Once we have file support, we can also add more reliable tests of the simulator that will not vary based on the compiler or machine used.