gitlab merge request webhook should trigger a try build

[dank]

gitlab is the new hotness, and its users want to see test results magically pop up as review comments on merge requests. Ideally they want to be able to paste the same webhook url into multiple projects and have it just work.

Buildbot does have gitlab webhook support, but only handles commits, not merge requests.

Here's a standalone rough draft I'm starting to use: ​http://kegel.com/buildbot/gateway-server.py.txt Once it's polished maybe it'd be worth including in contrib, but it'd be even better to integrate one into Buildbot's existing gitlab webhook handler.

[sa2ajj]

Dan, do you think you could submit a PR with this script in master/contrib? ("polished" is a bit vague qualifier; I think it's already good enough to land there.)

If not, I could do this on your behalf.

[dank]

I added posting results back to gitlab's gui and created a pull request, see ​https://github.com/buildbot/buildbot/pull/1812 against eight (since I'm a coward and haven't run nine yet).

See also bug 3333.

[dank]

I'm prototyping a new version of this. Here's a draft of doc changes describing the new version: ​https://github.com/dankegel/buildbot-x/commits/bug3254-gitlab-try-gateway-nine