Get available versions of the package.
        :return:

def _get_available_versions(self):
        '''
        Get available versions of the package.
        :return:
        '''
        solvables = self.zypper.nolock.xml.call('se', '-xv', self.name).getElementsByTagName('solvable')
        if not solvables:
            raise CommandExecutionError('No packages found matching \'{0}\''.format(self.name))

        return sorted(set([slv.getAttribute(self._attr_solvable_version)
                           for slv in solvables if slv.getAttribute(self._attr_solvable_version)]))