(RE-3302) Ensure rpm-builder modules have 3.7 enabled instead 3.4

As part of the effort to rename PE 3.4 to PE 3.7, this updates
'3.4' to '3.7' in the existing automation that manages rpm builders.
Merge pull request #95 from geoffnichols/RE-3302/master/update_rpm_builder_module_for_pe_37

(RE-3302) Ensure rpm-builder modules have 3.7 enabled instead 3.4