qitoolchain: better handling of cache
qitoolchain: better handling of cache

Even better: always print 'Adding package', print something
only when it make sense (extracting package takes a long time,
so we must let the use know what's going on)

Always add the package to the list of knwown pacakges, even if
it was not extracted
(this can otherwize leads to subtle bugs)

dmerejkowsky/qibuild,aldebaran/qibuild,dmerejkowsky/qibuild,dmerejkowsky/qibuild,aldebaran/qibuild,aldebaran/qibuild,dmerejkowsky/qibuild,aldebaran/qibuild,dmerejkowsky/qibuild