Chaos Engineering with gvisor

Hello there,

I wanted to ask whether there were any plans and/or appetite to include fault injection into this kernel? I'm interested in [Chaos Engineering](https://principlesofchaos.org) and this userspace kernel looks like a perfect place to expose some way to introduce failure.

In particular, I think that just adding fine-controlled delays and/or a certain amount of errors on particular syscalls would allow for a lot of valuable testing.

From reading the code, it looks like adding a layer like that would be both reasonably easy and cheap.

Please tell me if that's something that you'd be interested in accepting as a PR, and if you are, I'll follow up with a more detailed plan.

Also, the dev mailing list seems to be dominated with the automated messages, so I figured that an issue would be a better way to put this forward.

Thanks !

And btw, `gvisor` is pretty awesome, thanks for the hard work that went into it!