Support prefixes values for RPM.

Requires redline-rpm:1.1.15
Might actually work outside of test cases
Added additional test
Merge remote-tracking branch 'merscwog/prefixes' into add-prefixes. Also add a utility method and a merging of ospackage values.
Doc changes.
Merge pull request #24 from nebula-plugins/add-prefixes

Add prefixes to support relocatable rpms