Tags feature: support tags specification for NAT gateway (solves ansi…

…ble-collections#345)

- implements tags feature for NAT gateway
- adds integration test tasks for tags feature
- refactor integration tests (overall) removing hard-coded parameters
- add missing integration test tasks without CHECK_MODE

plugins/modules/ec2_vpc_nat_gateway.py

@@ -811,13 +811,11 @@ def pre_create(client, module, subnet_id, tags, purge_tags, allocation_id=None,
     changed = False
     err_msg = ""
     results = list()
-    
+
     check_input_tags(module, tags)
 
     if not allocation_id and not eip_address:
-        existing_gateways, allocation_id_exists = (
-            gateway_in_subnet_exists(client, subnet_id, check_mode=check_mode)
-        )
+        existing_gateways, allocation_id_exists = (gateway_in_subnet_exists(client, subnet_id, check_mode=check_mode))
         if len(existing_gateways) > 0 and if_exist_do_not_create:
             results = existing_gateways[0]
             results['tags'], tags_update_exists = ensure_tags(client, module, results['nat_gateway_id'], tags, purge_tags, check_mode)