Minor fixes in topology/generator.py
Minor fixes in topology/generator.py

netsec-ethz/scion,klausman/scion,FR4NK-W/osourced-scion,netsec-ethz/scion,FR4NK-W/osourced-scion,dmpiergiacomo/scion,dmpiergiacomo/scion,dmpiergiacomo/scion,klausman/scion,FR4NK-W/osourced-scion,dmpiergiacomo/scion,klausman/scion,Oncilla/scion,Oncilla/scion,Oncilla/scion,klausman/scion,klausman/scion,FR4NK-W/osourced-scion,Oncilla/scion,dmpiergiacomo/scion,netsec-ethz/scion,FR4NK-W/osourced-scion,dmpiergiacomo/scion,netsec-ethz/scion