mini-howto: set jessie to use sysvinit

[Dan Ritter <dsr@randomstring.org>]

Start by installing a clean jessie from debian-installer.

After boot:

# apt-get install sysv-rc sysvinit-core sysvinit-utils

# echo udev_log=\"err\" >> /etc/udev/udev.conf

# update-initramfs -k all -u

# shutdown -r now

when it reboots, it is running sysvinit:

$ pstree
init─┬─acpid
     ├─atd
     ├─cron
     ├─dhclient
     ├─exim4
     ├─5*[getty]
     ├─login───bash
     ├─rpc.idmapd
     ├─rpc.statd
     ├─rpcbind
     ├─rsyslogd─┬─{in:imklog}
     │          ├─{in:imuxsock}
     │          └─{rs:main Q:Reg}
     ├─sshd───sshd───sshd───bash───pstree
     └─udevd

For my sample KVM virtual machine, 1 cpu core and 512MB
allocated on a reasonably idle i5-2500 desktop:

boot time on a default install:  1.33s
boot time on a sysvinit without the udev.conf change: 32.18s
boot time on a sysvinit with the change: 1.37s.

Preventing systemd from being installed later is beyond the
scope of this mini-Howto.