fix get compute list via rest api, without datacenter specified
diff --git a/src/emuvim/api/rest/compute.py b/src/emuvim/api/rest/compute.py
index 9f0516b..1082a4d 100755
--- a/src/emuvim/api/rest/compute.py
+++ b/src/emuvim/api/rest/compute.py
@@ -106,10 +106,10 @@
 
     global dcs
 
-    def get(self, dc_label):
+    def get(self, dc_label=None):
         logging.debug("API CALL: compute list")
         try:
-            if dc_label == 'None':
+            if dc_label is None:
                 # return list with all compute nodes in all DCs
                 all_containers = []
                 for dc in dcs.itervalues():