Prepare capistrano/db migrations to support more setups (#2)

The following parameters have been added to deploy-secrets.yml:

* **use_rvm**: yes/no
* **ruby_version**: Ruby version for rvm. Defaults to 2.3.2
* **repository**: Git repository. Defaults to the oficial repository
* **branch**: Branch to deploy. Defaults to master
* **rails_env**: Defaults to the stage.

Fixed migrations that required admin rights. Now first check if the postgress extensions are available. If so finish without doing nothin.

Added support for passenger.

docker-compose.yml

@@ -35,6 +35,9 @@ services:
     volumes:
       - .:/var/www/consul:delegated
       - bundle:/usr/local/bundle:delegated
+      - "$SSH_AUTH_SOCK:/tmp/agent.sock"
+    environment:
+      - SSH_AUTH_SOCK=/tmp/agent.sock
 volumes:
   docker-example-postgres: {}
   bundle: {}