This commit updates external-snapshotter version to
v4.0.0 which supports snapshots v1.
Rook now defaults to enabling RBD and CephFS snapshotter
for K8s >= v1.17 and disabling it for K8s <= v1.16.
Supporting changes in documents and examples yaml files
are made.
Signed-off-by: Rakshith R <rar@redhat.com>