Enable ability to access mattermost API

Thanks for this great implementation. I've been playing around and got most things working.

Specifically, I wanted to test some calls to the mattermost API, such as:

curl -X POST -H "Content-Type: application/json" -d '{"login_id":"gitlab-username","password":"gitlab-password"}' "https://mattermost.k8s.mydomain.com/api/v3/users/login"

But it seems it's not able to reach the API end-point. I'm using the gitlab username and password I set up ... and since I opted to log in to mattermost with these, when enabling mattermost, as per the video, I assumed that these would be right credentials. Also, as per here, I don't think it's necessary to pass a team_id any longer.

{
  "id": "store.sql_user.get_for_login.app_error",
  "message": "We couldn't find an existing account matching your credentials. This team may require an invite from the team owner to join.",
  "detailed_error": "",
  "request_id": "s8zsjyp94ffctbojyqzcq9np9y",
  "status_code": 400
}

From the Headers, it may have something to do with nginx sitting in the middle. Ordinarily, if the step above was successful, the Headers would return a token.

content-length →264
content-type →application/json
date →Fri, 27 Jan 2017 14:51:32 GMT
server →nginx/1.11.3
status →400
strict-transport-security →max-age=15724800; preload
x-request-id →s8zsjyp94ffctbojyqzcq9np9y
x-version-id →3.6.0.3.6.1.d8a78293678fc8c68fbe985f8f83ae7c

If other debugging is happening with the mattermost set-up, as per #11 (closed), then it would be great to get this working too. Thanks.