Add timeout to build process

[freeman-lab]

We've had at least one case where a build failed to finish but also never reported an error, although this shouldn't happen, we should add a catchall timeout for builds just in case, as it's frustrating to be stuck with a repo and unable to rebuild.

[miykael]

Hi,

I seem to be a very skilled user, as I was able to get two different repos stuck in the build process. One is already mentioned in binder-project/binder-web#9, and the other one is based on the repo https://github.com/miykael/nipype_notebooks.

The second one seems to be stuck in limbo, because no new log messages are generated anymore. I'm not sure how I caused it to crash, but I know that the build created a big amount of log messages, as it tried to download 4GB from a rather slow external server.

I would appreciate a timeout for the build process or perhaps even a "force rebuild" or a "cancel build" button for the user.

Thank you for the amazing work, I really love mybinder.org and will do my best to not break it again.
Best,
Michael

[p-madden]

I also have two wedged builds that I cannot break out of. One has been in that state for three weeks. Is there any kind of manual workaround for this, however obscure? I considered renaming my repo, but since this has happened to two of the three binders I've created, I'm pessimistic about that being a useful approach.

[oroszl]

Just to note it here as well. I also have the same problem.