tests: use workspace-local directory for commitlog
tests: use workspace-local directory for commitlog

Can't rely on default /var/lib/scylla to be there or accessible.

avikivity/scylla,kjniemi/scylla,raphaelsc/scylla,kjniemi/scylla,avikivity/scylla,scylladb/scylla,scylladb/scylla,raphaelsc/scylla,kjniemi/scylla,duarten/scylla,duarten/scylla,scylladb/scylla,avikivity/scylla,raphaelsc/scylla,duarten/scylla,scylladb/scylla