Fix cassandra-stress commands calls (#1656)
Fix cassandra-stress commands calls (#1656)

since the change to add `STRESS_TEST_MARKER` to the command line,
seams like it's breaking the call to cassandra-stress when
client-encryption is used.

this simplifiy the command a bit, to a working state also for encrpytion.
scylladb/scylla-longevity-tests,scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests,scylladb/scylla-longevity-tests,scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests,scylladb/scylla-longevity-tests,scylladb/scylla-cluster-tests