testlib: No catch of custom exceptions in sandbox

Custom exceptions are not always properly pickled which could lead to
the sandbox test executor to crash when it tries to re __init__ pickled
exceptions thrown from the failed test.

Change-Id: I4e2ffe5802dda668b5d61c5a16e0989717121a04
Signed-off-by: Sean Wilson <spwilson27@gmail.com>
Reviewed-on: https://gem5-review.googlesource.com/12167
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>

tests,ext: Add a new testing library proposal

The new test library is split into two parts: The framework which resides
in ext/, and the gem5 helping components in /tests/gem5.

Change-Id: Ib4f3ae8d7eb96a7306335a3e739b7e8041aa99b9
Signed-off-by: Sean Wilson <spwilson2@wisc.edu>
Reviewed-on: https://gem5-review.googlesource.com/4421
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>