LVM: Add '--refresh' when activating volumes

LVM: Add '--refresh' when activating volumes

From `man 8 lvchange`:
  --refresh
      If the logical volume is active, reload its metadata. This is not
      necessary in normal operation, but may be useful ... if you're doing
      clustering manually without a clustered lock manager.

Fixes migration in a shared LVM (iscsi) setup, where a disk gets resized on one
node A and the guest is afterwards migrated to another node B: B still presents
the old size to the guest, leading to data corruption.

It is necessary to run `lvchange` twice because the options `-ay` and
`--refresh` are mutually exclusive.

Signed-off-by: Stoiko Ivanov <s.ivanov@proxmox.com>