added 4 tests regarding VirtualMachineGroups:
 * testVMgroupList, that tests if the expected list of groups is returned by the API
 * testVMgroupDetails, that tests if the expected virtual machine group is returned by the API
 * testWrongVMgroup, that test if a non existent VMgroup is asked, if a 404 itemNotFound returned
 * testgroupsDetails, that tests if the groups details are returned by the API