metrics: Fix NodeSelector with boolean values

When using a node selector with boolean values, e.g.:
```
apiVersion: sriovnetwork.openshift.io/v1
kind: SriovOperatorConfig
metadata:
  name: default
spec:
  configDaemonNodeSelector:
    feature.node.kubernetes.io/network-sriov.capable: "true"
```

the value needs to be quoted before forwarding it to the metrics-exporter
node selector field.

Fixes #766

Signed-off-by: Andrea Panattoni <apanatto@redhat.com>

bindata/manifests/metrics-exporter/metrics-daemonset.yaml

@@ -88,7 +88,7 @@ spec:
             readOnly: true
       nodeSelector:
         {{- range $key, $value := .NodeSelectorField }}
-          {{ $key }}: {{ $value }}
+          {{ $key }}: {{ $value | quote }}
         {{- end }}
       restartPolicy: Always
       volumes:

controllers/sriovoperatorconfig_controller_test.go

@@ -365,6 +365,33 @@ var _ = Describe("SriovOperatorConfig controller", Ordered, func() {
 					Expect(err).ToNot(HaveOccurred())
 				})
 
+				It("should deploy the sriov-network-metrics-exporter using the Spec.ConfigDaemonNodeSelector field", func() {
+					config := &sriovnetworkv1.SriovOperatorConfig{}
+					Expect(k8sClient.Get(ctx, types.NamespacedName{Namespace: testNamespace, Name: "default"}, config)).NotTo(HaveOccurred())
+
+					config.Spec.ConfigDaemonNodeSelector = map[string]string{
+						"node-role.kubernetes.io/worker": "",
+						"bool-key":                       "true",
+					}
+					err := k8sClient.Update(ctx, config)
+					Expect(err).NotTo(HaveOccurred())
+
+					DeferCleanup(func() {
+						Expect(k8sClient.Get(ctx, types.NamespacedName{Namespace: testNamespace, Name: "default"}, config)).NotTo(HaveOccurred())
+
+						config.Spec.ConfigDaemonNodeSelector = map[string]string{}
+						err := k8sClient.Update(ctx, config)
+						Expect(err).NotTo(HaveOccurred())
+					})
+
+					Eventually(func(g Gomega) {
+						metricsDaemonset := appsv1.DaemonSet{}
+						err = util.WaitForNamespacedObject(&metricsDaemonset, k8sClient, testNamespace, "sriov-network-metrics-exporter", util.RetryInterval, util.APITimeout)
+						Expect(err).NotTo(HaveOccurred())
+						Expect(metricsDaemonset.Spec.Template.Spec.NodeSelector).To((Equal(config.Spec.ConfigDaemonNodeSelector)))
+					}).Should(Succeed())
+				})
+
 				It("should deploy extra configuration when the Prometheus operator is installed", func() {
 					DeferCleanup(os.Setenv, "METRICS_EXPORTER_PROMETHEUS_OPERATOR_ENABLED", os.Getenv("METRICS_EXPORTER_PROMETHEUS_OPERATOR_ENABLED"))
 					os.Setenv("METRICS_EXPORTER_PROMETHEUS_OPERATOR_ENABLED", "true")