Completed ELBv2 implementation

IMPLEMENTATION_COVERAGE.md

@@ -2456,8 +2456,8 @@
 - [ ] update_distribution
 - [ ] update_streaming_distribution
 
-## elbv2 - 54% implemented
-- [ ] add_tags
+## elbv2 - 100% implemented
+- [X] add_tags
 - [X] create_listener
 - [X] create_load_balancer
 - [X] create_rule
@@ -2467,27 +2467,27 @@
 - [X] delete_rule
 - [X] delete_target_group
 - [X] deregister_targets
-- [ ] describe_account_limits
+- [X] describe_account_limits
 - [X] describe_listeners
-- [ ] describe_load_balancer_attributes
+- [X] describe_load_balancer_attributes
 - [X] describe_load_balancers
 - [X] describe_rules
-- [ ] describe_ssl_policies
-- [ ] describe_tags
-- [ ] describe_target_group_attributes
+- [X] describe_ssl_policies
+- [X] describe_tags
+- [X] describe_target_group_attributes
 - [X] describe_target_groups
 - [X] describe_target_health
-- [ ] modify_listener
-- [ ] modify_load_balancer_attributes
+- [X] modify_listener
+- [X] modify_load_balancer_attributes
 - [X] modify_rule
-- [ ] modify_target_group
-- [ ] modify_target_group_attributes
+- [X] modify_target_group
+- [X] modify_target_group_attributes
 - [X] register_targets
-- [ ] remove_tags
-- [ ] set_ip_address_type
+- [X] remove_tags
+- [X] set_ip_address_type
 - [X] set_rule_priorities
-- [ ] set_security_groups
-- [ ] set_subnets
+- [X] set_security_groups
+- [X] set_subnets
 
 ## sdb - 0% implemented
 - [ ] batch_delete_attributes