Revert^2 "Restrict to a single job at a time"

This reverts commit 75bdabe6d47fe9bd39945af7d544cb82580227dd.

Reason for revert: Jobs failed when 2+ ran.

Change-Id: I084ff451dd49a0dac47b4952671e8b5e31618c86

nodepool/nodepool.yaml

diff --git a/nodepool/nodepool.yaml b/nodepool/nodepool.yaml
index 4e60c4d..e751f0b 100644
--- a/nodepool/nodepool.yaml
+++ b/nodepool/nodepool.yaml
@@ -21,7 +21,7 @@
         key: ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQDaTT3+Y6dIh221ZsQ0ki6VwGb6lzd1/CvIS8RX6ZNmxJTXS7UKlvhAVTbGQPtmjdIQbwUyEqZEvIm/bUBr7dNbyeMLiRiRtoN+u1Quq8OAes2N7nUKnjLjGjVnM2mvYHGWHRDbpAQCtmXtbiQkHkfLLzewb+MqntQZ57xap31qriTkv4rdnlMN4kElILb5E/8WOAAJXYrt3b1TrTXwZUx7is1OTa38I9jJTpUMCn2otWGH9LlfeUhz/z8ZPB21wgUZN9CF5NwwBanqCNXy0jHiumOGx9e7Hc7apt641KiDuRt0aWyE6No/aMe6hVYnFR3NMG3rBtortXl+R5birK8l zuul
     pools:
       - name: main
-        max-servers: 4
+        max-servers: 1
         use-internal-ip: True
         # Gate node readiness on SSH/host-key-scan reachability
         # (nodepool's GCE default). With this enabled nodepool verifies a node