Support check_run for Github/Cirrus

[bdrewery]

Adds support for https://developer.github.com/v3/activity/events/types/#checkrunevent which allows Cirrus events to display.

There's plenty of room for improvement here but it works for now.

• There's some "check_suite" event that also comes through that isn't very useful as far as I can tell.
• The lack of showing the git hash can be confusing when multiple runs are involved. The PR URL is not sent unless the PR is from the same repo. This flaw exists in the existing "status" hook as well. I think most of the notifications should include a shortened hash and branch name.

Example output (with verbose queued enabled):

12:28:42 <@    gitlogs>| [poudriere] Check Run for freebsd11 Queued. https://cirrus-ci.com/task/5662741731213312            
12:33:12 <@    gitlogs>| [poudriere] Check Run for freebsd11 completed: Success. https://cirrus-ci.com/task/5662741731213312

12:33:56 <@    gitlogs>| [poudriere] Check Run for freebsd11 queued. https://cirrus-ci.com/task/5654801989238784              
12:34:07 <@    gitlogs>| [poudriere] Check Run for freebsd11 completed: Cancelled. https://cirrus-ci.com/task/5654801989238784

12:39:18 <@gitlogs> [poudriere] bdrewery opened pull request #725: TEST - https://git.io/JectH                              
12:39:19 <@    gitlogs>| [poudriere] Check Run for freebsd11 queued. https://cirrus-ci.com/task/5152479666241536            
12:39:21 <@    gitlogs>| [poudriere] Check Run for freebsd12 queued. https://cirrus-ci.com/task/6278379573084160            
12:49:23 <@    gitlogs>| [poudriere] Check Run for freebsd12 completed: Success. https://cirrus-ci.com/task/6278379573084160
12:52:28 <@    gitlogs>| [poudriere] Check Run for freebsd11 completed: Success. https://cirrus-ci.com/task/5152479666241536

[TkTech]

Looks good from a quick skim, thanks for the contribution. I need to add some tests for github but this should go live on n.tkte.ch on Saturday.