core: don't check for vm.getVdsGroupId on import vm

ImportVmCommand shouldn't expect a value in vm.getVdsGroupId
as it is supplied in the parameters separately.

Change-Id: I21610313a85fa52a14b1ddf15b20e2ca73944e06
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1095223
Signed-off-by: Omer Frenkel <ofrenkel@redhat.com>