core: remove unneeded call to lock vm in db on import vm

On import VM, we add the VM to the DB in ImageLocked status, so we don't
need to call VmHandler.lockVm afterwards.

Change-Id: I331f7d350bf7cd044a7b4ff64e9376963fd5ec9b
Signed-off-by: Arik Hadas <ahadas@redhat.com>