The *install-packages.service* unit has to be enabled, and the condition
checking for `/etc/ignition/packages.installed` was inverted.
Sending standard output to the console as well as the journal allows
watching progress.
Some machines may need to install multiple packages for separate use
cases. Requiring each use case to define a systemd unit that runs
`rpm-ostree install` directly would be cumbersome and also quite slow,
as each one would have to run in turn. Instead, now there is a single
*install-packages.service* which installs all of the packages listed in
files in `/etc/ignition/packages.d`. On first boot, all files in that
directory are read and all the packages they list will be installed in a
single `rpm-ostree install` invocation.
Dustin