API.login - don't show popup on 503
API.login - don't show popup on 503

means any caller of API.login needs to be able to deal with 503 Service Unavailable

https://bugzilla.redhat.com/show_bug.cgi?id=1468252

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