fixed error message for releasing an ip when not waiting for the nat …

…gateway to delete successfully 1st

cloud/amazon/ec2_vpc_nat_gateway.py

@@ -655,7 +655,7 @@ def release_address(client, allocation_id, check_mode=False):
     """
     err_msg = ''
     if check_mode:
-        return True
+        return True, ''
 
     ip_released = False
     params = {
@@ -977,13 +977,13 @@ def remove(client, nat_gateway_id, wait=False, wait_timeout=0,
         err_msg = str(e)
 
     if release_eip:
-        eip_released, err = (
-            release_address(client, allocation_id, check_mode=check_mode)
+        eip_released, eip_err = (
+            release_address(client, allocation_id, check_mode)
         )
         if not eip_released:
             err_msg = (
                 "{0}: Failed to release EIP {1}: {2}"
-                .format(err_msg, allocation_id, err)
+                .format(err_msg, allocation_id, eip_err)
             )
             success = False