Currently QEMU exits with code 0 on both panic an shutdown. For tests
it is useful to return 1 on panic, so that it counts as a test
failure.

Introduce a new exit-failure PanicAction that makes main() return
EXIT_FAILURE. Tests can use -action panic=exit-failure option to
activate this behavior.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Message-Id: <20220725223746.227063-2-iii@linux.ibm.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>