Use array union operator to get rid of the duplicates.

https://bugzilla.redhat.com/show_bug.cgi?id=1160848
Add test cases for the duplicate columns.

https://bugzilla.redhat.com/show_bug.cgi?id=1160848
region_number/region_description are only intended to be declared on the class immediately under AR::Base.

https://bugzilla.redhat.com/show_bug.cgi?id=1160848
Merge pull request #1114 from lfu/double_columns_1160848

Use array union operator to remove the duplicates.