blackbox_exporter: add setcap for net_raw
Without this:
setcap 'cap_net_raw+ep' $(which blackbox_exporter)
All ICMP probes will fail. At the moment we fix this manually by issuing the setcap call after every upgrade. I suggest to add this by default to the packaging, as it is a core functionality of the blackbox exporter.
Ping @Leo - what do you think?