Switch celery keys to be all-uppercase

[Christopher Allan Webber]

Celery will finally be moving to a structure that will be much,
much easier for combining with MediaGoblin. Horray!

http://ask.github.com/celery/internals/app-overview.html

In order to better prepare for this, we should switch our config
system setup for celery's configuration to also have all
celery-relevant keys to be ALL\_UPPERCASE in form.

So a few changes:


-  Update mediagoblin/config\_spec.ini and set all keys to
   UPPERCASE form.
-  Update mediagoblin/init/celery/**init.**.py 's
   setup\_celery\_from\_config and remove the force-to-upper... well
   maybe anyway! I suppose it doesn't hurt to include this, but it
   isn't necessary any more.

This is a simple, bitesized task, appropriate for a new
contributor.