Move all of NixOS to nixos/ in preparation of the repository merge

nixos/lib/qemu-flags.nix

@@ -0,0 +1,10 @@
+# QEMU flags shared between various Nix expressions.
+
+{
+
+  qemuNICFlags = nic: net: machine:
+    [ "-net nic,vlan=${toString nic},macaddr=52:54:00:12:${toString net}:${toString machine},model=virtio"
+      "-net vde,vlan=${toString nic},sock=$QEMU_VDE_SOCKET_${toString net}"
+    ];
+
+}