Allow owner of pull request to cancel a long running build

[vbjay]

If I submit a pull request to a repo on github, and I realize I need to tweak yaml file to make it not stuck, I'd like to be able to cancel the current build if it is related to my pull request. So adding a cancel link in the build page if I can authenticate that I am the user that pushed that pull request. I should not be able to manage other pull requests by other users.

[FeodorFitsner]

Sounds like a good suggestion!