tests: Python regression scripts using new print function

Change-Id: I92060da4537e4ff1c0ff665f2f6ffc3850c50e88
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Giacomo Gabrielli <giacomo.gabrielli@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/8892
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>

config: Make configs/common a Python package

Continue along the same line as the recent patch that made the
Ruby-related config scripts Python packages and make also the
configs/common directory a package.

All affected config scripts are updated (hopefully).

Note that this change makes it apparent that the current organisation
and naming of the config directory and its subdirectories is rather
chaotic. We mix scripts that are directly invoked with scripts that
merely contain convenience functions. While it is not addressed in
this patch we should follow up with a re-organisation of the
config structure, and renaming of some of the packages.

test, arm: Add scripts to test checkpoints

Add a set of scripts to automatically test checkpointing in the
regression framework. The checkpointing tests are similar to the
switcheroo tests, but instead of switching between CPUs, they
checkpoint the system and restore from the checkpoint again. This is
done at regular intervals, typically while booting Linux.

The implementation is fairly straight forward, with the exception that
we have to work around gem5's inability to restore from a checkpoint
after a system has been instantiated. We work around this by forking
off child processes that does the actual simulation and never
instantiate a system in the parent process unless a maximum checkpoint
count is reached (in which case we just simulate the system to
completion in the parent).

Checkpoint testing is currently only enabled 32- and 64-bit ARM
systems using atomic CPUs.

Note: An unfortunate side-effect of forking is that every new process
will overwrite the stats and terminal output from the previous
process. This means that the output directory only contains data from
the last checkpoint.