tests: update lvmcache-exercise

To handle multiple VGs with the same name.
Simply using the VG name is ambiguous, and
lvmetad requires the VG uuid be used to
specify which one is meant.

test/shell/lvmcache-exercise.sh

@@ -18,12 +18,20 @@ aux prepare_pvs 5
 vgcreate $vg1 "$dev1"
 vgcreate $vg2 "$dev3" "$dev4" "$dev5"
 
+UUID1=$(get vg_field $vg1 uuid)
+
 aux disable_dev "$dev1"
 pvscan
 # dev1 is missing
 fail pvs $(cat DEVICES)
 
+# create a new vg1 on dev2,
+# so dev1 and dev2 have different VGs with the same name
 vgcreate $vg1 "$dev2"
+
+UUID2=$(get vg_field $vg1 uuid)
+
+# Once dev1 is visible again, both VGs named "vg1" are visible.
 aux enable_dev "$dev1"
 
 pvs "$dev1"
@@ -36,9 +44,15 @@ lvconvert --yes --repair $vg2/$lv1
 aux enable_dev "$dev3"
 
 # here it should fix any reappeared devices
-lvs $vg1 $vg2
+lvs
 
 lvs -a $vg2 -o+devices 2>&1 | tee out
 not grep reappeared out
 
+# This removes the first "vg1" using its uuid
+vgremove -ff -S vg_uuid=$UUID1
+
+# This removes the second "vg1" using its name,
+# now that there is only one VG with that name.
 vgremove -ff $vg1 $vg2
+