handle date clearing for pfDatepicker

Author: vkrizan

src/form/datepicker/datepicker.directive.js

@@ -56,7 +56,7 @@ angular.module('patternfly.form').directive('pfDatepicker', function () {
       element.datepicker('update', $scope.date);
 
       //Change happened on the date picker side. Update the underlying date model
-      element.datepicker($scope.date).on('changeDate', function (elem) {
+      element.datepicker($scope.date).on('changeDate clearDate', function (elem) {
         $scope.$apply(function () {
           $scope.date = elem.date;
         });