* Always for Immutable selector in Deployment Replicaset Daemonset
With extensions/v1beta1 removed there is no need of a special case
to check for Spec.Selector immutability.
The ValidateImmutableField is now moved into the
Validate[Resource]Update method, tests for v1beta1 are removed and test
for v1 are added.
Validation tests were updated to reflect the changes,
mostly decoupling other fields changes from selectors and creating a
dedicated case to test selector immutability.
* Move validation inside appropriate function
* Fix validation tests