systemc: Make the test config retrieve sc_main results.

systemc: Make the test config retrieve sc_main results.

Accellera's implementation prints any sc_report which is thrown and
escapes sc_main, so we need to do the same to make some tests pass.
Arguably gem5 should fail if sc_main reports an error, but verify.py
would interpret that as the test failing too, and some tests
purposefully generate errors.

This change also stops using the logging module. It wasn't really
providing any benefit, and added extra decoration to log messages
which confused verify.py.

Change-Id: I6850d0ada5e477b67527d99d421478586cda93b3
Reviewed-on: https://gem5-review.googlesource.com/12254
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>