Dialog seeding changes necessary for the service dialog yaml import.

https://bugzilla.redhat.com/show_bug.cgi?id=1163875

Productization requires service dialog import files to be linked into
the manageiq dialog import folder.
Changed dialog seeding to accommodate sub-directories and added tests.
Merge pull request #1091 from tinaafitz/service_dialog_seed_changes

Dialog seeding changes necessary for the service dialog yaml import.