Legacy config reader doesn't transform between FORM_FACTOR and DeviceInfo's device type
ubuntu-touch-session.d files define FORM_FACTOR in terms of Hostnamed's Chassis value [1]. We, however, have our own set of values. So we have to convert between these values.
[1] https://www.freedesktop.org/software/systemd/man/org.freedesktop.hostname1.html#Semantics