Fixing ExistsAndWarnIfChanges so that it will allow a user to pass

This PR implmenents a new custom error that is returned when a task
lifecycle set to fi.LifecycleExistsAndWarnIfChanges. This will allow
a task to to fail validation, but the task is marked as completed and
the error is cleared.

upup/pkg/fi/context.go

@@ -127,11 +127,12 @@ func (c *Context) Render(a, e, changes Task) error {
 			case LifecycleExistsAndValidates:
 				return fmt.Errorf("Lifecycle set to ExistsAndValidates, but object was not found")
 			case LifecycleExistsAndWarnIfChanges:
-				return fmt.Errorf("Lifecycle set to ExistsAndWarnIfChanges, but object was not found")
+				return NewExistsAndWarnIfChangesError("Lifecycle set to ExistsAndWarnIfChanges and object was not found.")
 			}
 		} else {
 			switch *lifecycle {
 			case LifecycleExistsAndValidates, LifecycleExistsAndWarnIfChanges:
+
 				out := os.Stderr
 				changeList, err := buildChangeList(a, e, changes)
 				if err != nil {
@@ -239,3 +240,19 @@ func (c *Context) AddWarning(task Task, message string) {
 	c.warnings = append(c.warnings, warning)
 	glog.Warningf("warning during task %s: %s", task, message)
 }
+
+// ExistsAndWarnIfChangesError is the custom error return for fi.LifecycleExistsAndWarnIfChanges.
+// This error is used when an object needs to fail validation, but let the user proceed with a warning.
+type ExistsAndWarnIfChangesError struct {
+	msg string
+}
+
+// NewWarnIfInsufficientAccessError is a builder for ExistsAndWarnIfChangesError.
+func NewExistsAndWarnIfChangesError(message string) *ExistsAndWarnIfChangesError {
+	return &ExistsAndWarnIfChangesError{
+		msg: message,
+	}
+}
+
+// ExistsAndWarnIfChangesError implementation of the error interface.
+func (e *ExistsAndWarnIfChangesError) Error() string { return e.msg }

upup/pkg/fi/executor.go

@@ -105,6 +105,15 @@ func (e *executor) RunTasks(taskMap map[string]Task, maxTaskDuration time.Durati
 		for i, err := range taskErrors {
 			ts := tasks[i]
 			if err != nil {
+				//  print warning message and continue like the task succeeded
+				if _, ok := err.(*ExistsAndWarnIfChangesError); ok {
+					glog.Warningf(err.Error())
+					ts.done = true
+					ts.lastError = nil
+					progress = true
+					continue
+				}
+
 				remaining := time.Second * time.Duration(int(ts.deadline.Sub(time.Now()).Seconds()))
 				glog.Warningf("error running task %q (%v remaining to succeed): %v", ts.key, remaining, err)
 				errors = append(errors, err)