Fix bug where ./scion.sh lint would always return 0
Fix bug where ./scion.sh lint would always return 0

The sort pipe meant the return value from flake8 was lost. Using `set -o
pipefail` fixes that.

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