initial commit oif iniit_switch
fix for config, allow specifying target for cloud-init --single
fix path to systemd
add some doc to module
exit and warn if no 'dpkg' (probably wrong distro)
add ubuntu-init-switch module for testing sysvinit.

The module is useful primarily for testing in Ubuntu's transition to systemd.
It should be very harmless elsewhere as it defaults to doing nothing,
and will only run if configured as 'ubuntu' distro *and* 'dpkg' is available.