Use Python 3.x compatible syntax constructs

Avoid print operator, deprected except and
other things covered by statical checks.

Change-Id: I89f9608b977b2d4567300ec82558284dac347c9a
diff --git a/tempest/common/rest_client.py b/tempest/common/rest_client.py
index 531dfc8..e94455d 100644
--- a/tempest/common/rest_client.py
+++ b/tempest/common/rest_client.py
@@ -144,8 +144,8 @@
             try:
                 auth_data = json.loads(resp_body)['access']
                 token = auth_data['token']['id']
-            except Exception, e:
-                print "Failed to obtain token for user: %s" % e
+            except Exception as e:
+                print("Failed to obtain token for user: %s" % e)
                 raise
 
             mgmt_url = None