add disks to the list of possible source images
match a disk label in image selection

if the case arises, prefer custom disks to std images
Allow user to specify a disk id, for an image
Revert "Allow user to specify a disk id, for an image"

We do not want user to pass ids, do not introduce that use
This reverts commit 610b18fc683370eac7233a9e157b68641f2ddbb5.
Merge pull request #27 from kalou/customimage

Allow user to select an existing disk to use as disk source image during vm creation