Make looponfail support listen to forward inotify over virtualbox

[craigds]

When using virtualbox (using vboxsf filesystem, or NFS, or ...) there's no way to forward filesystem events from the host to the guest. So filesystem events like inotify don't work, and hence xdist looponfail doesn't work.

A clever solution is to run listen on the host and forward the events to the guest over TCP. The caveat is that the application needs to know how to interpret the events. Guard does this for rails development:

http://jamie.ideasasylum.com/2014/02/efficiently-using-guard-vagrant-rails-development/

[RonnyPfannschmidt]

@craigds supporting something like that ould be considered if there would be a fs event package with multiple backends and the ability to autoconfigure

its absolutely certainly not something i want to invent just for pytest-xdist

additionally we currently do not use inotify