Memberships: Use external volume, remove one from the Helm chart.

Change-Id: Ie2afcd9ab28a12e7d6bea6375a96e00a0f63b525
diff --git a/charts/memberships/templates/install.yaml b/charts/memberships/templates/install.yaml
index 1d0034b..dee0f59 100644
--- a/charts/memberships/templates/install.yaml
+++ b/charts/memberships/templates/install.yaml
@@ -64,4 +64,4 @@
       volumes:
       - name: memberships
         persistentVolumeClaim:
-          claimName: memberships
+          claimName: {{ .Values.volumeClaimName }}