Fix policy logging (#1416)
Fix policy logging (#1416)

Before: 'Segment dropped due to path policy: Unwanted AS(%s): %s f056531e3b80, 2018-02-22 14:00:35+00:00, 1-11 70'
After: 'Segment dropped due to path policy: Unwanted AS(1-11): f056531e3b80, 2018-02-22 14:02:11+00:00, 1-11 70'
Oncilla/scion,netsec-ethz/scion,Oncilla/scion,klausman/scion,klausman/scion,netsec-ethz/scion,Oncilla/scion,klausman/scion,netsec-ethz/scion,klausman/scion,netsec-ethz/scion,klausman/scion,Oncilla/scion