Fix privileges on /var/run/libvirt directory

Fix privileges on /var/run/libvirt directory

Previous commit

  commit 32a9aac2e04c991340b66c855a1095e4e6445e54
  Author: William Jon McCann <william.jon.mccann@gmail.com>
  Date:   Thu May 3 12:36:27 2012 -0400

    Use XDG Base Directories instead of storing in home directory

Accidentally changed the umask when creating /var/run/libvirt
to 077. This prevents /var/run/libvirt being readable by non-root,
which is required for non-root to connect to libvirtd. Fix the
code so that umask 077 is only used for the non-privileged libvirtd
instance.