Copy unicorn.conf.erb from main cookbooks.

Change-Id: I177d7bdfa69dd3c86e7a6a6ea7752c352b2a8990
Make unicorn reload dotenv in before_exec.

Will make our zero-downtime deploys pick up changes to ENV files.

Change-Id: I96e99d1794968d80d59258d544b876c0701b3392