root context redirect should be a 307

Currently, if somebody comes in on /root-context, Undertow automatically redirects to /root-context/. This causes problems with non-GET requests, i.e.

1. POST /root
2. 302
3. Browser turns this in GET /root/
4. Form data lost.

This is causing a lot of user reported problems around our SAML adapter if users don't add a trailing '/' to the registered SAML endpoint URL.