'Convert SELF.GROUP to is stringed numerical value suitable for dscl.'

def _make_group_numerical(self):

    if (self.group is None):
        self.group = 'nogroup'
    try:
        self.group = grp.getgrnam(self.group).gr_gid
    except KeyError:
        self.module.fail_json(msg=('Group    "%s"    not    found.    Try    to    create    it    first    using    "group"    module.' % self.group))
    self.group = str(self.group)
