initial iso_importer work

(cherry picked from commit 4e9bc6433c596cfddc7eb23d43fe81c026049779)
using runcible iso modules
(cherry picked from commit 48fd47c21d4fbaf2cb407fc198b6371e716a4a67)
migrating to storing content_Type in the repo object
(cherry picked from commit 94133486760327e61225146bf75c77247fc8f2bd)
ensuring content_type is preserved across clone
localizing message for repo content type
Merge pull request #2108 from jlsherrill/iso_importer_split

properly supporting ISO importers and distributors in pulp