Fix: filter unsupported source type from volume list

For disk attachment, isos should not be listed,
and cdrom should just accept isos.

Signed-off-by: Royce Lv <lvroyce@linux.vnet.ibm.com>
Reject improper format for storage types

Reject non-iso storage volume for cdrom attachment,
and non supported format types for disk attachment

Signed-off-by: Royce Lv <lvroyce@linux.vnet.ibm.com>