My answer above was not accurate. Actually, on my system the startup only succeeds with:
$ cd janusgraph-full-0.6.1
$ bin/janusgraph.sh start
So, it fails when you start it the way you did:
$ janusgraph-full-0.6.1/bin/janusgraph.sh start -v
Your way does work for v0.5.3 but not for v0.6.0 and v0.6.1. I will report it as an issue, if not already present.