hostnamectl: add a chassis symbol in status output

The idea is to be able to distinguish whether we're in a VM/container or something
more substantial at a glance.
         Chassis: laptop 💻
         Chassis: tablet 具
         Chassis: vm 🖴
         Chassis: server 🖳
         Chassis: handset 🕻
         Chassis: watch ⌚
         Chassis: desktop 🖥️
         Chassis: container ☐