fix clean_instances_aws() to actully terminate instances
fix clean_instances_aws() to actully terminate instances

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