ubuntu@murdoch:~/charm-repo/layers/vanilla$ echo 'Override' > templates/site.conf 
ubuntu@murdoch:~/charm-repo/layers/vanilla$ charm build
build: Composing into /home/ubuntu/charm-repo
build: Processing layer: layer:basic
build: Processing layer: layer:apache-php
build: Processing layer: vanilla
build: Processing interface: http
build: Processing interface: mysql
ubuntu@murdoch:~/charm-repo/layers/vanilla$ cat /home/ubuntu/charm-repo/trusty/vanilla/templates/site.conf 
Override
ubuntu@murdoch:~/charm-repo/layers/vanilla$