kvm: set cpu topology only if cpucore per socket is positive value (#4527)

This PR fixes a regression issue in #4497

In cloudstack 4.14 or before, the cpu topology is set only when cpucore per socket is set (to 4 or 6).
in other conditions, there is no cpu topology in vm xml definition.

with #4497, vm will have cpu topology in its xml definition, if cpucore per socket is not set.

    <topology sockets='<vm cpu cores>' cores='1' threads='1'/>
Not sure if it causes any issue. I think it would be better not to add this part in vm xml definition if cpucore per socket is not set.

Author: ustcweizhou

plugins/hypervisors/kvm/src/main/java/com/cloud/hypervisor/kvm/resource/LibvirtComputingResource.java

@@ -4239,10 +4239,10 @@ private void setCpuTopology(CpuModeDef cmd, int vcpus, Map<String, String> detai
                 numCoresPerSocket = 6;
             } else if (vcpus % 4 == 0) {
                 numCoresPerSocket = 4;
-            } else {
-                numCoresPerSocket = 1;
             }
         }
-        cmd.setTopology(numCoresPerSocket, vcpus / numCoresPerSocket);
+        if (numCoresPerSocket > 0) {
+            cmd.setTopology(numCoresPerSocket, vcpus / numCoresPerSocket);
+        }
     }
 }