CoreOS: Disable unused services

This patch is masking the services that are started when the Ironic
Python Agent ramdisk boots up but are not needed. Consequently, this may
save us some seconds at startup time.

The list of services disabled are: update-engine, update-engine-stub,
resize-btrfs, locksmithd, fleet and etcd.

Change-Id: Ib91ec2d0c69b1724170d38dea5d38248145c5d9f

imagebuild/coreos/oem/cloud-config.yml

@@ -17,6 +17,24 @@ coreos:
     - name: media-configvirtfs.mount
       mask: true
 
+    - name: update-engine.service
+      mask: true
+
+    - name: update-engine-stub.service
+      mask: true
+
+    - name: resize-btrfs.service
+      mask: true
+
+    - name: locksmithd.service
+      mask: true
+
+    - name: fleet.service
+      mask: true
+
+    - name: etcd.service
+      mask: true
+
     - name: ironic-python-agent-embed-ssh-keys.service
       command: start
       content: |