upgrade cass-operator to 1.6.0 (#41)

I replaced the all-in-one operator manifest file with separate files in part
to make the updates a little easier.

go.mod

@@ -3,7 +3,7 @@ module github.com/k8ssandra/reaper-operator
 go 1.15
 
 require (
-	github.com/datastax/cass-operator v1.5.1-0.20210112050706-a45fd80b40e0
+	github.com/datastax/cass-operator v1.6.0
 	github.com/go-logr/logr v0.1.0
 	github.com/k8ssandra/reaper-client-go v0.3.0
 	github.com/onsi/ginkgo v1.12.1

test/config/cass-operator/cluster_role.yaml

@@ -0,0 +1,14 @@
+apiVersion: rbac.authorization.k8s.io/v1
+kind: ClusterRole
+metadata:
+  name: cass-operator-cr
+rules:
+  - apiGroups:
+      - ""
+    resources:
+      - nodes
+      - persistentvolumes
+    verbs:
+      - get
+      - list
+      - watch

test/config/cass-operator/cluster_role_binding.yaml

@@ -0,0 +1,13 @@
+kind: ClusterRoleBinding
+apiVersion: rbac.authorization.k8s.io/v1
+metadata:
+  name: cass-operator-crb
+subjects:
+  - kind: ServiceAccount
+    name: cass-operator
+    # The namespace is removed here in order for it to be set by kustomize. See
+    # https://github.com/kubernetes-sigs/kustomize/pull/166 for details.
+roleRef:
+  kind: ClusterRole
+  name: cass-operator-cr
+  apiGroup: rbac.authorization.k8s.io