Add E2 class machines

Google has requested that we use these instead of the N-class.

Change-Id: I9881c00a1a008161b6e94380d878c860eccb9e64
diff --git a/nodepool/nodepool.yaml b/nodepool/nodepool.yaml
index b9d1906..2f7dfea 100644
--- a/nodepool/nodepool.yaml
+++ b/nodepool/nodepool.yaml
@@ -43,6 +43,19 @@
             instance-type: n1-standard-16
             cloud-image: debian-stretch
             volume-size: 40
+          - name: debian-stretch-e2-standard-2
+            instance-type: e2-standard-2
+            cloud-image: debian-stretch
+            volume-size: 40
+          - name: debian-stretch-e2-standard-8
+            instance-type: e2-standard-8
+            cloud-image: debian-stretch
+            volume-size: 40
+          - name: debian-stretch-e2-standard-16
+            instance-type: e2-standard-16
+            cloud-image: debian-stretch
+            volume-size: 40
+
 labels:
   - name: debian-stretch-8G
     min-ready: 0
@@ -56,3 +69,9 @@
     min-ready: 0
   - name: debian-stretch-n1-standard-16
     min-ready: 0
+  - name: debian-stretch-e2-standard-2
+    min-ready: 0
+  - name: debian-stretch-e2-standard-8
+    min-ready: 0
+  - name: debian-stretch-e2-standard-16
+    min-ready: 0