ccm logs not being collected to nightlies

At least some of the time, Jenkins is failing to collect ccm logs and is uploading a zero byte tar archive to nightlies, for example: https://nightlies.apache.org/cassandra/trunk/Cassandra-trunk-dtest/1100/Cassandra-trunk-dtest/label=cassandra-dtest,split=5/

09:25:06 + tar -cJf ccm_logs.tar.xz './tmp//test//logs/*'
09:25:06 tar: ./tmp//test//logs/*: Cannot stat: No such file or directory
09:25:06 tar: Exiting with failure status due to previous errors