sprinkler-image: bunch of cleanup.

* Use whatever system manager the distro specifies
* Install cron
* Only install beaglebone getting started on a beaglebone
distro: Add systemd distro configuration

While here, set default VIRTUAL_RUNTIME settings, such as
login manager and init manager.
Switch to new packagegroup.

Don't like avahi being forced upon us. It brings in dbus and other
un-fun things. Use different task-basic provider.
techworks-version: add recipe

Based on angstrom-version, add /etc/os-release and
/etc/techworks-version to the build.
Add techworks-version to boot package group.
Update techworks distro:

Use Linaro toolchain
Add sample local.conf and bblayers.conf
Use local timezone
packagegroup: add g-multi to default usbgadget group