tests: use vgscan after enable_dev

Since our test environment runs also in non-real-udev world,
it's using  /etc/.cache file with scanned files.

So in this case it is mandatory the user runs 'vgscan'
after a device reappears in the system.

This 'first' lvm2 command then fixes metadata (just like vgs did).

test/shell/unlost-pv.sh

@@ -48,7 +48,11 @@ check_ not
 aux disable_dev "$dev1"
 vgreduce --removemissing --force $vg
 aux enable_dev "$dev1"
-vgs 2>&1 | grep 'Removing PV'
-vgs 2>&1 | not grep 'Removing PV'
+
+vgscan 2>&1 | tee out
+grep 'Removing PV' out
+
+vgs 2>&1 | tee out
+not grep 'Removing PV' out
 
 vgremove -ff $vg