pkg-stats: add luarocks perl python virtual infrastructures

Recognize the recently added infrastructures: luarocks, perl, python,
virtual.

Signed-off-by: Fabio Porcedda <fabio.porcedda@gmail.com>
Cc: Jerzy Grzegorek <jerzy.grzegorek@trzebnica.net>
Cc: Luca Ceresoli <luca@lucaceresoli.net>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Acked-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>