Get rid of on_at format in format_timezone
Get rid of on_at format in format_timezone

The format is in essence the same as the 'gtl' format.
(transferred from ManageIQ/manageiq@eb988a1e13fcd929fedcbbde414bc7e8045ef1e0)

ManageIQ/manageiq-ui-classic,ManageIQ/manageiq-ui-classic,ManageIQ/manageiq-ui-classic,ManageIQ/manageiq-ui-classic