Simplify deploy secrets example configuration file

So now it's similar to our database example file.

config/deploy-secrets.yml.example

@@ -1,18 +1,17 @@
-staging:
-  deploy_to: "/home/deploy/consul"
-  ssh_port: "21"
-  server: "staging.consul.es"
-  user: "deploy"
-
-preproduction:
-  deploy_to: "/home/deploy/consul"
-  ssh_port: "2222"
-  server: xxx.xxx.xxx.xxx
-  user: "deploy"
-
-production:
+default: &default
   deploy_to: "/home/deploy/consul"
   ssh_port: "22"
+  user: "deploy"
+
+staging:
+  <<: *default
+  server: "staging.consul.es"
+
+preproduction:
+  <<: *default
+  server: xxx.xxx.xxx.xxx
+
+production:
+  <<: *default
   server: xxx.xxx.xxx.xxx
   server2: xxx.xxx.xxx.xxx
-  user: "deploy"