Do not replace the IP if an error was raised

If an error is raised when submitting the form, we should keep the IP
that was entered.

JIRA INFRA-285

app/static/js/hosts.js

@@ -49,7 +49,9 @@ $(document).ready(function() {
   // - add interface
   // Do NOT replace the IP on edit interface page load!
   // (we have to keep the existing IP)
-  if( $("#hostForm").length || $("#interfaceForm").length ) {
+  // Do NOT replace the IP if the form was submitted and an error was raised
+  // (we should display the same value that was submitted)
+  if( ($("#hostForm").length || $("#interfaceForm").length) && ! $("input").hasClass("is-invalid") ) {
     set_default_ip();
   }