Save /usr/html before running bats tests, restore afterwards (Fixes #46)
Save /usr/html before running bats tests, restore afterwards (Fixes #46)

Tested by running "make build", then inspecting /usr/html in the resulting image
and verifying that it's the original nginx 50x.html and index.html files.

fancyremarker/docker-nginx,apnarm/docker-nginx,aptible/docker-nginx,aptible/docker-nginx,apnarm/docker-nginx,100health/docker-nginx,aptible/docker-nginx,fancyremarker/docker-nginx,100health/docker-nginx