Added missing 'forest_delete' route

https://bugzilla.redhat.com/show_bug.cgi?id=1163382
https://bugzilla.redhat.com/show_bug.cgi?id=1163384

@dclarizio please review/test.
Steps to Reproduce:
1. Go to Configuration/Configure
2. Select Current server in Settings Accordion
3. Go to Authentication tab
4. change mode to LDAP
5. Check the checkbox for "Get User Groups from LDAP"
6. In "Trusted Forest Settings" box, click on + sign to Add a new forest
7. Enter new Forest details and then press "Add this entry" button.