tests/qtest: qtest_qemu_args

tests/qtest: qtest_qemu_args

Define an accessor that returns all the arguments used to exec QEMU.
Collect the arguments that were passed to qtest_spawn_qemu, plus the trace
arguments that were composed inside qtest_spawn_qemu, and move them to a
new function qtest_qemu_args.

This will be needed to test the cpr-exec migration mode.

Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Link: https://lore.kernel.org/qemu-devel/1759332851-370353-11-git-send-email-steven.sistare@oracle.com
Signed-off-by: Fabiano Rosas <farosas@suse.de>