Merge pull request #878 from mckern/1.5.x

(maint) Add RHEL7 to list of mocks to build against
Merge pull request #879 from mckern/1.5.x

(maint) Point RHEL7 build_default entry to x86_64, not i386
(maint) Updated RHEL7 support in 1.5.x branch

These changes should fix packaging for RHEL7 and allow RPMs to
be cleanly assembled again.