tests: Fix the stats unit test.

This has been broken since February. The interface for opening
initializing where the stats output should go was changed, but the
test wasn't updated.

Change-Id: I54bd8be15bf870352d5fcfad95ded28d87c7cc5a
Reviewed-on: https://gem5-review.googlesource.com/6001
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>

python: Move native wrappers to the _m5 namespace

Swig wrappers for native objects currently share the _m5.internal name
space with Python code. This is undesirable if we ever want to switch
from Swig to some other framework for native binding (e.g., PyBind11
or Boost::Python). This changeset moves all of such wrappers to the
_m5 namespace, which is now reserved for native code.

Change-Id: I2d2bc12dbc05b57b7c5a75f072e08124413d77f3
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Curtis Dunham <curtis.dunham@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>

unittest: Make unit tests capable of using swig and python, convert stattest