Use a real certificate2.Product in tests cases.

It's just a data object, so no need to stub or
mock it yet.
Test cases for empty,none,not set brand type/name

Also split the is_rhel_branded_product() tests to a
seperate test class.
Cleanup entbranding tests names.

Make it more clear what tests are using default or
unset values ('none') vs not having that attribute ('no')

Make it more explicit that ent cert Product is not
exactly the same as installed Product (the latter
always have brand_type/brand_name set to None)
Merge pull request #928 from candlepin/alikins/more_branding_tests

Alikins/more branding tests