UI: don't allow to add an empty ldap forest entry
UI: don't allow to add an empty ldap forest entry

The LDAP hostname has to be set -- we cannot be adding a new forest
entry without an LDAP hostname to the set of existing LDAP hosts.

https://bugzilla.redhat.com/show_bug.cgi?id=1177015
(transferred from ManageIQ/manageiq@9a4b554c952faf37dfc66b475c5b24beaf48f93c)

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