test: forcefully clean up old loop devices.

sometimes these can get left around, and udev can be looking
at them at awkward times so they don't disappear.
So be forceful.

Signed-off-by: NeilBrown <neilb@suse.de>

test

@@ -94,6 +94,14 @@ do_setup() {
   trap cleanup 0 1 3 15
   trap ctrl_c 2
 
+  # make sure there are no loop devices remaining.
+  # udev started things can sometimes prevent them being stopped
+  # immediately
+  while grep loop /proc/partitions > /dev/null 2>&1
+  do
+    losetup -d /dev/loop[0-9]* 2> /dev/null
+    sleep 1
+  done
   devlist=
   for d in 0 1 2 3 4 5 6 7 8 9 10 11 12 13
   do