Make sure the umask is 022.

Without this various things get installed as root and are unusable once
running as a normal user.  This is unfortunately the case of all Python
packages, as they don't use `install' or a package format that preserves
file permissions.  This also affects various other random files created
during initial setup, such as /etc/polkit-1/rules.d/50-libvirt-$USER.rules
and others.