storageVolWipePattern: Don't take shortcut to refreshPool()

storageVolWipePattern: Don't take shortcut to refreshPool()

In d16f803d780 we've tried to solve an issue that after wiping an
image its format might have changed (e.g. from qcow2 to raw) but
libvirt wasn't probing the image format. We fixed this by calling
virStorageBackendRefreshVolTargetUpdate() which is what
refreshPool() would end up calling. But this shortcut is not good
enough because the function is called only for local types of
volumes (like dir, fs, netfs). But now that more backends support
volume wiping we have to call the function with more caution.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Pavel Hrdina <phrdina@redhat.com>