[UNDERTOW-38] Update EmptyRoleSemantic handle to handle a middle ground of authenticate only.

This change introduces a new EmptyRoleSemantic enumeration that includes a middle ground of still requiring authentication where no roles are defined.

This is needed for integration scenarios such as JBossWS where it is desirable to mandate authentication but where authorization checking will be handled in a different container, using pure servlet spec configuration authentication and authorization are enabled as a pair.

JBoss AS will also require the following change when this pull request is merged before AS can be updated to an Undertow version containing this change: -

https://github.com/darranl/jboss-as/commit/2da13e650cb53d6e55b0e892c569102c8b89662b