preserve ownerships in /run

[milahu]

/run/screen should be owned by root:utmp

currently /run/screen is owned by nobody:nogroup which makes screen fail with

Directory '/run/screen' must have mode 777.

good

$ screen -v
Screen version 4.05.00 (GNU) 10-Dec-16

$ screen -d -m -S test

$ screen -x test -X hardcopy out.txt

$ stat /run/screen | head -n4
  File: /run/screen
  Size: 1020      	Blocks: 0          IO Block: 4096   directory
Device: edh/237d	Inode: 89          Links: 51
Access: (0775/drwxrwxr-x)  Uid: (    0/    root)   Gid: (   43/    utmp)

bad

$ nix-shell -p hello

[nix-shell:~]$ # screen -d -m -S test

[nix-shell:~]$ screen -x test -X hardcopy out.txt
Directory '/run/screen' must have mode 777.

[nix-shell:~]$ stat /run/screen | head -n4
  File: /run/screen
  Size: 1020      	Blocks: 0          IO Block: 4096   directory
Device: 0,237	Inode: 89          Links: 51
Access: (0775/drwxrwxr-x)  Uid: (65534/  nobody)   Gid: (65534/ nogroup)

see also https://github.com/ev3dev/ev3dev/issues/391