Limit Nodepool to 4 servers

We have a 72vcpu quota, and nodepool does not have support for
automatically detecting the quota in GCE yet.  If we request too
many, nodepool will return an error.  Until we improve the GCE
driver in nodepool to handle this automatically, limit our usage
to 4 servers, which should stay under the quota since our largest
usage is 16vcpus.

Change-Id: Ic7d08593889891ded4aec8114594c068f5330f42
diff --git a/nodepool/nodepool.yaml b/nodepool/nodepool.yaml
index f2e6d29..b9d1906 100644
--- a/nodepool/nodepool.yaml
+++ b/nodepool/nodepool.yaml
@@ -16,7 +16,7 @@
         key: ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQDaTT3+Y6dIh221ZsQ0ki6VwGb6lzd1/CvIS8RX6ZNmxJTXS7UKlvhAVTbGQPtmjdIQbwUyEqZEvIm/bUBr7dNbyeMLiRiRtoN+u1Quq8OAes2N7nUKnjLjGjVnM2mvYHGWHRDbpAQCtmXtbiQkHkfLLzewb+MqntQZ57xap31qriTkv4rdnlMN4kElILb5E/8WOAAJXYrt3b1TrTXwZUx7is1OTa38I9jJTpUMCn2otWGH9LlfeUhz/z8ZPB21wgUZN9CF5NwwBanqCNXy0jHiumOGx9e7Hc7apt641KiDuRt0aWyE6No/aMe6hVYnFR3NMG3rBtortXl+R5birK8l zuul
     pools:
       - name: main
-        max-servers: 8
+        max-servers: 4
         use-internal-ip: True
         labels:
           - name: debian-stretch-8G