Add debian-stretch-8G label

This is probably a good starting point for a VM for real jobs.  It
has 8GB of ram, 2vcpus, and 40GB of disk.

Change-Id: Ib68bdaf43f450fd957bc5bdb568a77b648baba27
diff --git a/nodepool/nodepool.yaml b/nodepool/nodepool.yaml
index 819d500..a164dcb 100644
--- a/nodepool/nodepool.yaml
+++ b/nodepool/nodepool.yaml
@@ -24,6 +24,13 @@
             cloud-image: debian-stretch
             volume-type: standard
             volume-size: 10
+          - name: debian-stretch-8G
+            instance-type: n1-standard-2
+            cloud-image: debian-stretch
+            volume-type: standard
+            volume-size: 40
 labels:
   - name: testlabel
     min-ready: 1
+  - name: debian-stretch-8G
+    min-ready: 1