package/quagga: Fix directories and permissions

Quagga runs as the "quagga" user, but it also needs to modify files
in /etc and /var - config files, pid files and vty sockets for vtysh.

Tell the configure script the right folders to use, create the
user, fix the permissions, and then let systemd know (if needed).

Signed-off-by: Nathaniel Roach <nroach44@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>