some improvements to resize procedure

show how to find the PV and resize it, that was omitted!

howto/ganeti.md

@@ -179,7 +179,17 @@ Then the filesystem needs to be resized inside the VM:
 
     ssh root@test1.torproject.org 
 
-Use lvs to display information about logical volumes:
+Use `pvs` to display information about the physical volumes:
+
+    root@cupani:~# pvs
+    PV         VG        Fmt  Attr PSize   PFree   
+    /dev/sdc   vg_test   lvm2 a--  <8.00g  1020.00m
+
+Resize the physical volume to take up the new space:
+
+    pvresize /dev/sdc
+
+Use `lvs` to display information about logical volumes:
 
     # lvs
     LV            VG               Attr       LSize    Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert