When creating the trove datastore, get the guest image id from glance.
The trove guest image gets uploaded along with all the other
images specified in $IMAGE_URLS. It is not necessary to upload
it again in init_trove.
Also: add xenapi case to stackrc for trove guest image
Closes-Bug: 1339818
Change-Id: I2973af27ab93182fcd674f874daba1036d767d52