There are two reason why this is useful:

1. less code to vendor into external users of the framework

The following dependencies become obsolete due to this change (from `dep`):

(8/23) Removed unused project github.com/grpc-ecosystem/go-grpc-prometheus
(9/23) Removed unused project github.com/coreos/etcd
(10/23) Removed unused project github.com/globalsign/mgo
(11/23) Removed unused project github.com/go-openapi/strfmt
(12/23) Removed unused project github.com/asaskevich/govalidator
(13/23) Removed unused project github.com/mitchellh/mapstructure
(14/23) Removed unused project github.com/NYTimes/gziphandler
(15/23) Removed unused project gopkg.in/natefinch/lumberjack.v2
(16/23) Removed unused project github.com/go-openapi/errors
(17/23) Removed unused project github.com/go-openapi/analysis
(18/23) Removed unused project github.com/go-openapi/runtime
(19/23) Removed unused project sigs.k8s.io/structured-merge-diff
(20/23) Removed unused project github.com/go-openapi/validate
(21/23) Removed unused project github.com/coreos/go-systemd
(22/23) Removed unused project github.com/go-openapi/loads
(23/23) Removed unused project github.com/munnerz/goautoneg

2. works around https://github.com/kubernetes/kubernetes/issues/75338
   which currently breaks vendoring

Some recent changes to crd_util.go must now be pulling in the broken
k8s.io/apiextensions-apiserver packages, because it was still working
in revision 2e90d92d (as demonstrated by
https://github.com/intel/pmem-CSI/tree/586ae281ac2810cb4da6f1e160cf165c7daf0d80).