webadmin: VM GuideMe - update dialog on attach disk

VM Guide Me:
Update 'Configure Virtual Disks' button to
'Add another Virtual Disk' after attaching a disk.

Change-Id: I21f7f8b7cd0733b2b2fc06cbe7cc39a9a42b755e
Bug-Url: https://bugzilla.redhat.com/1026308
Signed-off-by: Daniel Erez <derez@redhat.com>