Ubuntu fix for uncreated run directory.

Because the directory is not created, PXE installations fails with
waiting *.install files and rebooting again.
I've got no link but looking at my debian vserver it's the case for debian and ubuntu that all folders on ```/var/run``` are chmoded to ```0755```.

```
# ll /var/run/
total 36K
drwxr-xr-x 13 root       root        440 May  1 23:03 ./
drwxr-xr-x 23 root       root       4.0K Mar 11 18:03 ../
drwxr-xr-x  2 root       root         40 May 16 13:32 console/
drwxr-xr-x  2 root       root         60 Jun 30 15:48 ConsoleKit/
-rw-r--r--  1 root       root          5 Feb 14 13:59 console-kit-daemon.pid
-rw-r--r--  1 root       root          5 Feb 14 13:57 crond.pid
----------  1 root       root          0 Feb 14 13:57 crond.reboot
drwxr-xr-x  2 messagebus messagebus   80 Feb 14 13:57 dbus/
prw-------  1 root       root          0 Feb 14 13:57 initctl|
drwxrwxrwt  2 root       root         60 May  5 18:40 lock/
-rw-r--r--  1 root       root         87 Feb 14 13:57 motd.dynamic
drwxr-xr-x  2 root       root         60 Feb 14 13:57 mount/
drwxr-xr-x  2 root       root         60 Feb 14 13:57 network/
-rw-r--r--  1 root       root          6 Apr 29 22:11 nginx.pid
-rw-r--r--  1 root       root          5 Apr 29 22:11 ntpd.pid
drwxr-x---  2 www-data   www-data    120 Apr 29 22:11 php5-fpm/
drwxrwxr-x  3 root       utmp         60 Feb 14 13:59 screen/
drwxr-xr-x  2 root       root         40 Feb 14 13:57 sendsigs.omit.d/
drwxrwxrwt  2 root       root         60 Feb 14 13:57 shm/
drwxr-xr-x  2 root       root         40 Feb 14 13:57 sshd/
-rw-r--r--  1 root       root          5 Feb 14 13:57 sshd.pid
-rw-rw-r--  1 root       utmp       4.9K Jun 30 15:48 utmp
```