tests: remove debug.log in enable_dev

In aux functions we may drop debug log from
last running lvm command - so we do not
get debug log from properly executed command,
when we fail here.

test/lib/aux.sh

@@ -393,6 +393,7 @@ disable_dev() {
 enable_dev() {
 	local dev
 
+	rm -f debug.log
 	init_udev_transaction
 	for dev in "$@"; do
 		local name=$(echo "$dev" | sed -e 's,.*/,,')