Do not accept validation for empty states

We used to do this to not fail on creating proposals, but it's not
needed anymore (and wrong).
Use validate_one_for_role helper instead of custom code
Call super in initialize for model

This is needed to initialize some internal variables.
Drop unneeded localized strings
Check that HAE repos are available if running on SUSE
Assume that repos are missing if attribute is not set
Merge pull request #6 from vuntz/validation-fixes

Some cleanups + check that HAE repos are available