JS add_flash - add optional id, ensure uniqueness when given
JS add_flash - add optional id, ensure uniqueness when given

authentication failed message now gets an id of auth_failed, and removes the previous one if a new one with the same id is added

https://bugzilla.redhat.com/show_bug.cgi?id=1327042
(transferred from ManageIQ/manageiq@1f0c710f5f9536ea9c7341efefad9130de7ee16c)

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