Improve pool validations a bit

robottelo/hosts.py

@@ -1518,13 +1518,14 @@ def register_to_cdn(self, pool_ids=None):
         # Attach a pool only if the Org isn't SCA yet
         sub_status = self.subscription_manager_status().stdout
         if SM_OVERALL_STATUS['disabled'] not in sub_status:
-            if pool_ids is None:
+            if pool_ids in [None, []]:
                 pool_ids = [settings.subscription.rhn_poolid]
-            cmd_result = self.subscription_manager_attach_pool(pool_ids)[0]
-            if cmd_result.status != 0:
-                raise ContentHostError(
-                    f'Error during pool attachment, command output: {cmd_result.stdout}'
-                )
+            for pid in pool_ids:
+                int(pid, 16)  # raises ValueError if not a HEX number
+            cmd_result = self.subscription_manager_attach_pool(pool_ids)
+            for res in cmd_result:
+                if res.status != 0:
+                    raise ContentHostError(f'Pool attachment failed with output: {res.stdout}')
 
     def ping_host(self, host):
         """Check the provisioned host status by pinging the ip of host