pre-upgrade job to verify function references and restricted privileges for fetcher and builder SA (#717)

It is mandatory (from this release onwards) for function to refer to secrets, config-maps and packages in its own namespace to ensure isolation of users sharing the same cluster.
This change runs a pre-upgrade job to verify function references for all functions created prior to this release and fails the upgrade by printing a list of functions that violate this restriction.

preupgradechecks/main.go

@@ -0,0 +1,66 @@
+/*
+Copyright 2016 The Fission Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package main
+
+import (
+	"os"
+
+	"github.com/docopt/docopt-go"
+	log "github.com/sirupsen/logrus"
+
+	"github.com/fission/fission"
+)
+
+func getStringArgWithDefault(arg interface{}, defaultValue string) string {
+	if arg != nil {
+		return arg.(string)
+	} else {
+		return defaultValue
+	}
+}
+
+func main() {
+	usage := `Package to perform operations needed prior to fission installation
+Usage:
+  pre-upgrade-checks --fn-pod-namespace=<podNamespace> --envbuilder-namespace=<envBuilderNamespace>
+Options:
+  --fn-pod-namespace=<podNamespace>                        Namespace where function pods get deployed.
+  --envbuilder-namespace=<envBuilderNamespace>             Namespace where builder env pods are deployed.`
+
+	arguments, err := docopt.Parse(usage, nil, true, fission.BuildInfo().String(), false)
+	if err != nil {
+		log.Fatalf("Error: %v", err)
+	}
+
+	functionPodNs := getStringArgWithDefault(arguments["--fn-pod-namespace"], "fission-function")
+	envBuilderNs := getStringArgWithDefault(arguments["--envbuilder-namespace"], "fission-builder")
+
+	crdBackedClient, err := makePreUpgradeTaskClient(functionPodNs, envBuilderNs)
+	if err != nil {
+		log.Printf("Error creating a crd client : %v, please retry helm upgrade", err)
+		os.Exit(1)
+	}
+
+	if !crdBackedClient.IsFissionReInstall() {
+		log.Printf("Nothing to do since CRDs are not present on the cluster")
+		return
+	}
+
+	crdBackedClient.VerifyFunctionSpecReferences()
+	crdBackedClient.RemoveClusterAdminRolesForFissionSAs()
+	crdBackedClient.SetupRoleBindings()
+}