test: Use wait_until to ensure ping goes out
test: Use wait_until to ensure ping goes out

Intermittent failure evident here:
https://travis-ci.org/bitcoin/bitcoin/jobs/344021180

Github-Pull: #12545
Rebased-From: 0eb84f30d80847b7392ad42b2d916eaf5923a63c

chaincoin/chaincoin,chaincoin/chaincoin,chaincoin/chaincoin,chaincoin/chaincoin,chaincoin/chaincoin,chaincoin/chaincoin