Configure the Cinder StorPool driver for iSCSI.

Pass the iscsi_export_to and iscsi_portal_group options to Cinder.
In the future, if we ever support a protocol value other than "iscsi",
these parameters will be made conditional on that.

Change-Id: I70ad0adcd2ea925279b72dd29f85f69bd2e59b38
diff --git a/config.yaml b/config.yaml
index 74237ab..a0bce89 100644
--- a/config.yaml
+++ b/config.yaml
@@ -59,3 +59,8 @@
     default:
     description: |
       Authentication token for the StorPool API.
+  iscsi-portal-group:
+    type: string
+    default:
+    description: |
+      The name of the iSCSI portal group that volumes should be exported to.