update gitlab to latest version (#343)

* update gitlab to latest version

This should refer to the offical docker compose file of gitlab: https://gitlab.com/gitlab-org/omnibus-gitlab/blob/master/docker/docker-compose.yml

* added option to select gitlab external_url prefix

This is needed so that rancher will put a correct uri scheme prefix to the ${gitlab_hostname} to the external_url.

* added external_url prefix

honestly i don't know if `${gitlab_omnipus_prefix}${gitlab_hostname}` will work since i cannot test it by myself right now, but imo that should work....

* changed version to latest

since image is going to be gitlab/gitlab-ce:latest, the version here inside the readme should reflect this.

* update to latest

templates/gitlab/0/rancher-compose.yml

@@ -1,6 +1,6 @@
 .catalog:
   name: Gitlab Community
-  version: 8.5.1-0
+  version: latest
   description: |
     Gitlab CE is a free GitHub alternative
   minimum_rancher_version: v0.56.0
@@ -8,11 +8,21 @@
   uuid: gitlab-0
   questions:
     - variable: "gitlab_hostname"
-      description: "Gitlab hostname"
+      description: "Gitlab hostname (without uri scheme http:// or https://)"
       label: "Hostname:"
       required: true
       default: "git.example.com"
       type: "string"
+    - variable: "gitlab_omnipus_prefix"
+      label: "Gitlab external_url prefix:"
+      description: |
+        This is needed for the docker-compose file to set the correct external_url
+      default: 'https://'
+      required: true
+      type: "string"
+      options:
+        - 'https://'
+        - 'http://'
     - variable: "http_port"
       description: "HTTP port to expose on host. Will be used to bind TCP"
       label: "HTTP port:"