clean up bootstrap

gce-properties.yml

diff --git a/gce-properties.yml b/gce-properties.yml
index b694930..e58ad12 100644
--- a/gce-properties.yml
+++ b/gce-properties.yml
@@ -1,7 +1,8 @@
 ---
 credentials_file: ~/.apigee-secure/default-service-account.json
 machine_type: 'n1-standard-4'
-image: 'centos-7'
+image: 'centos-7-v20180104'
+#image: 'centos-7'
 #image: 'centos-7-v20170918'
 #image: 'centos-7-v20160511'
 #image: 'centos-6-v20170918'