Fixes #6553/BZ111225: add "repositories" to product resource type name.

There was some confusion about Repository permissions being underneath
Products.  This commit simply updates the resource type name to make
it obvious that repositories are also affected by these permissions.

http://projects.theforeman.org/issues/6553
https://bugzilla.redhat.com/show_bug.cgi?id=1112255
That's what I originally had and it sounded odd to me to have Repository singular but I'm fine with either.