core: cleanup AddVmParameters constructors

In order to generalize AddVmParameters for AddVmCommand +
AddVmFromTemplate + AddVmFromScratch, the list of disks and storage
domain ID are removed from the arguments lists of the constructors.
Those values can be set by using the setter methods when needed.

Change-Id: I06f2de3db1b0559af4df04d0d158b10b8460c684
Signed-off-by: Arik Hadas <ahadas@redhat.com>