Fix listing bug in node info

Fixes a listing bug during 'node info -l' introduced in previous
commit 4a3780cf as a "cleanup", and makes this a little more
elegant.

References #12

pvc.py

@@ -1339,9 +1339,10 @@ def get_vm_list(hypervisor, limit):
                 exit(1)
         # Check hypervisor to avoid unneeded ZK calls
         vm_hypervisor[vm] = zk_conn.get('/domains/{}/hypervisor'.format(vm))[0].decode('ascii')
-        if hypervisor != None and vm_hypervisor[vm] == hypervisor:
+        if hypervisor == None:
             vm_list.append(vm)
         else:
+            if vm_hypervisor[vm] == hypervisor:
                 vm_list.append(vm)
 
     # Gather information for printing