Teach kano-updater to migrate Kanux repository

 * Defined new transition migrations from 1.1 and 1.2 to 1.3
   where Kanux repo will be changed with a sed command

 * I am pretty sure I am missing some actions on this module,
   can't see where the preupdate scenarious are being called from,
   but pychecker seems to be happy, extracted code works ok.
missing python os module
migrate_repo fixed
Merge pull request #12 from KanoComputing/migrate-repo-dns

Teach kano-updater to migrate Kanux repository