webadmin: AddVmFromTemplate - remove redundant logic

Removing redundant logic from VmListModel -> onSave():
for getting selected storage domains / allocation policies,
DisksAllocationModel -> getImageToDestinationDomainMap()
should be passed to AddVmFromTemplateParameters.

Change-Id: I1eb9157cbf692a8de4e5751390ed925310bdf4a0
Signed-off-by: Daniel Erez <derez@redhat.com>