fix(save_email_data): move perf test email_data.json into logdir
fix(save_email_data): move perf test email_data.json into logdir

the default was to save it to SCT main direcotry, and that can
be shared with multiple parallel jobs

scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests