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

tests/integration/targets/ec2_vpc_nat_gateway/tasks/main.yml

@@ -15,7 +15,7 @@
 # As we use the same EIP, I think changed should be false (if this is correct, lines 194-218 are redundant and 
 # lines 177 and 190 should report `not create_ngw.changed`).
 #
-#`Delete NAT gateway` in teh always block throws `(DependencyViolation) when calling the DeleteVpc operation`  
+#`Delete NAT gateway` in always block throws `(DependencyViolation) when calling the DeleteVpc operation`  
 #  ============================================================
 
 - name: ec2_vpc_nat_gateway tests