Create a /run/piaware/upgrader.pid pidfile for the duration of an upgrade.
Create a /run/piaware/upgrader.pid pidfile for the duration of an upgrade.

The prerm script will look for this to see if it can safely stop piaware
(e.g. an upgrade invoked from the command line), or if it should let it
run and restart itself later (for upgrades invoked via piaware).

flightaware/piaware,flightaware/piaware