Fix django-admin commands

Some django-admin commands used to inherit from django’s NoArgsCommand.
Therefore their implementation was placed in handle_noargs() method.

A previous commit has changed the django-admin commands all over synnefo to
inherit from SynnefoCommand (which inherits from django’s BaseCommand),
without changing the implementation method to handle().
As a result, these commands fail with NotImplementedError.

This commit fixes this issue.

Closes #103