Add ready field to Job status

to keep a count of the pods that have the ready condition.

Also:
- Add feature gate JobReadyPods.
- Add Ready to describe.

Change-Id: Ib934730a430a8e2a2f485671e345fe2330006939

pkg/apis/batch/validation/validation.go

@@ -186,6 +186,9 @@ func validateJobStatus(status *batch.JobStatus, fldPath *field.Path) field.Error
 	allErrs = append(allErrs, apivalidation.ValidateNonnegativeField(int64(status.Active), fldPath.Child("active"))...)
 	allErrs = append(allErrs, apivalidation.ValidateNonnegativeField(int64(status.Succeeded), fldPath.Child("succeeded"))...)
 	allErrs = append(allErrs, apivalidation.ValidateNonnegativeField(int64(status.Failed), fldPath.Child("failed"))...)
+	if status.Ready != nil {
+		allErrs = append(allErrs, apivalidation.ValidateNonnegativeField(int64(*status.Ready), fldPath.Child("ready"))...)
+	}
 	if status.UncountedTerminatedPods != nil {
 		path := fldPath.Child("uncountedTerminatedPods")
 		seen := sets.NewString()