collect_active_ip crashes when prefix ids has been changed

[John-Magne Bredal]

collect_active_ip stores references to prefix ids in rrd_file. When a prefix has changed id, the reference is wrong and the script tries to create a new tuple for the rrdfile. This will trigger the unique constraint on rrd_file.filename and the script crashes.

1. Make the script do a rollback on such errors.
2. Use prefix.netaddr as reference to prefix in stead of prefix.id
3. Make sure the old references are removed.

[John-Magne Bredal (john-m-bredal)]

Fix: https://nav.uninett.no/hg/stable/rev/fada39841319

[John-Magne Bredal (john-m-bredal)]

Fix here: https://nav.uninett.no/hg/stable/rev/fada39841319
and here: https://nav.uninett.no/hg/stable/rev/31f99d93439b