tests: suppress output on switcheroo tests

tests: suppress output on switcheroo tests

The output from the switcheroo tests is voluminous and
(because it includes timestamps) highly sensitive to
minor changes, leading to extremely large updates to the
reference outputs.  This patch addresses this problem
by suppressing output from the tests.  An internal
parameter can be set to enable the output.  Wiring that
up to a command-line flag (perhaps even the rudimantary
-v/-q options in m5/main.py) is left for future work.