Undertow default host response headers incorrectly added to load balancer configurations

Undertow response headers are always set (added/updated) when migrating Undertow subsystem configurations, yet not all Undertow subsystem configurations, e.g. load-balancers, should have these set.

The correct behaviour should be to only update existent headers, except when migrating a legacy jboss web configuration to undertow, in such case the response headers should be added.