tester: Tell cassandra stress to contact only the first node ip
tester: Tell cassandra stress to contact only the first node ip

According to Shlomi:
"""cassandra-stress is using a smart driver
so when it connects to any node in the cluster
it will get the complete toplogy of the cluster
and connect to every node based on its needs -
which is all the nodes for a load"""

Signed-off-by: Benoît Canet <ecd1f14f7c1c6dc7a40210bdcc3810e0107ecbc8@scylladb.com>

scylladb/scylla-cluster-tests,amoskong/scylla-cluster-tests,scylladb/scylla-cluster-tests,amoskong/scylla-cluster-tests,amoskong/scylla-cluster-tests,amoskong/scylla-cluster-tests,amoskong/scylla-cluster-tests,scylladb/scylla-longevity-tests,scylladb/scylla-cluster-tests,scylladb/scylla-longevity-tests,scylladb/scylla-cluster-tests,scylladb/scylla-longevity-tests,scylladb/scylla-cluster-tests