repo codingStyle fixes

- repo step and unit tests are now pep8 compliant
- fixed camelCase for repo step parameters
- removed usage of properties as input of the step.
  Its now job of use to choose which property name he wants via renderable
- added test on repo download from changesource
- update doc and release notes

Signed-off-by: Pierre Tardy <pierre.tardy@intel.com>