Cleaner output if sections are empty

Even with a completely empty config we still get the following output:

root
  sysinfo
    load: 0.87/0.92/0.98
    ram: 243/168/0
    uptime: 1d 22:18:19
  netdev
  ping
  file
  shellcmd

With this patch the sections are skipped if there are no entries and the
command no sysinfo can be used to skip displaying the system
information.

Change-Id: I429fe7626b43aef74ff7458f5c2864888fa9a562
5 files changed