Clear error messages on form fields on change

The class "is-invalid" is removed on all type=text input
on keyup event.

JIRA INFRA-285

app/static/js/csentry.js

+$(document).ready(function() {
+
+  // When an invalid input was submitted, the server
+  // adds the "is-invalid" class to form fields to display
+  // them in red with an error message
+  // When starting to type again, we want to remove the error
+  // message to not confuse the user
+  $('input[type="text"]').keyup(function(event) {
+    $(this).removeClass("is-invalid");
+  });
+
+});

app/static/js/hosts.js

@@ -71,6 +71,10 @@ $(document).ready(function() {
   $("#name").keyup(function(event) {
     var hostname = $(this).val();
     $("#interface_name").val(hostname);
+    // If an invalid hostname was submitted, the interface name
+    // will be invalid as well
+    // Remove the invalid messages when starting typing a new name
+    $("#interface_name").removeClass("is-invalid");
   });
 
   // Fill MAC address on page load

app/templates/base.html

@@ -65,5 +65,6 @@
   <script type=text/javascript>
     $SCRIPT_ROOT = {{ request.script_root|tojson|safe }};
   </script>
+  <script src="{{ url_for('static', filename='js/csentry.js') }}"></script>
   {% block csentry_scripts %}{% endblock %}
 {% endblock %}