core: remove redundant checks when running vm

Three checks are removed from RunVmCommand#initVm:
1. Check if the VM is null
2. Check if snapshot is being taken for the VM
3. Check if the VM status is not imageLocked or imageIllegal

Those checks are already tested in the canDoAction method (by the
validations that are made by RunVmValidator), and since the VM is
locked in the execute phase, it should be enough.

Change-Id: I396b3322c551af3414268f5fe16a1ccaf5ccf1bd
Signed-off-by: Arik Hadas <ahadas@redhat.com>