docker: install iperf in tester container
docker: install iperf in tester container

GitOrigin-RevId: a38176a7ccd39ba4132343059da0b8349882d00a

netsec-ethz/scion,Oncilla/scion,Oncilla/scion,netsec-ethz/scion,Oncilla/scion,Oncilla/scion,netsec-ethz/scion,netsec-ethz/scion