Support underscore headers in ingress

Nginx's configuration has the underscore header value disabled.
When uploading image, glance api uses underscore header.
For example, x-image-meta-disk_format or x-image-meta_name.

Change-Id: I86e7f7d8d908904a4e45fa68f6bd613028d45801

ingress/templates/deployment-ingress.yaml

@@ -75,6 +75,7 @@ spec:
           args:
             - /nginx-ingress-controller
             - '--default-backend-service=$(POD_NAMESPACE)/ingress-error-pages'
+            - --configmap=$(POD_NAMESPACE)/nginx-custom-configuration
 {{- if .Values.network.host_namespace }}
           volumeMounts:
             - name: ingress-etc

ingress/templates/nginx-custom-configuration.yaml

@@ -0,0 +1,7 @@
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: nginx-custom-configuration
+data:
+  enable-underscores-in-headers: "true"
+