Change FileDepot ::SUPPORTED_DEPOTS to #supported_depots

Build a hash of subclass => display_name for all descendants
https://bugzilla.redhat.com/show_bug.cgi?id=965889
Update drop-down to to get the correct uri_prefix based on the model

https://bugzilla.redhat.com/show_bug.cgi?id=965889
Add support_case and depot_name to the edit screen where appropriate

https://bugzilla.redhat.com/show_bug.cgi?id=965889
Add reverse relationship for MiqServer#log_file_depot

https://bugzilla.redhat.com/show_bug.cgi?id=965889
Create log_file_depot using relationships

https://bugzilla.redhat.com/show_bug.cgi?id=965889
Simplify all the things

https://bugzilla.redhat.com/show_bug.cgi?id=965889
Ensure that all FileDepots are subclassed

https://bugzilla.redhat.com/show_bug.cgi?id=965889