Store the driver top-level DSOs to /run/opengl-driver

[picnoir]

Idea of @soupglasses

We would still modify the rpaths to point to /var/lib

Pros:

• Can use Nix binaries without wrapping them first.
• Fixes the wrapper startup overhead.

Cons:

• Need something to keep /run/opengl-driver in sync.
  • We can do that using the package managers hooks. That means we have to distribute nix-gl-host through the host package manager though.
  • We can do that using a nix-distributed daemon epolling the top-level DSOs.