[Popover] Fix onRequestClose called 3 times

[oliviertassinari]

@chrismcv Could you review this PR. I think that It's also solving #2346

[chrismcv]

@oliviertassinari - this pretty much looks good. There is one case that we have with nested popovers that it doesn't support. Using a div layer in render-to-layer https://github.com/callemall/material-ui/pull/2346/files#diff-6adf2b35daa69784d26ee7e0f8289abbR64 sorts this - but it does require a prop closeOnClickAway to be passed through from the popover. Happy for you to merge this, and I can resubmit a PR for just render-to-layer.

[oliviertassinari]

Thanks, I'm merging this one, and I'm waiting for your PR.