sdcm.cluster: Only register cleanup functions if 'failure_post_behavior' == 'destroy'
sdcm.cluster: Only register cleanup functions if 'failure_post_behavior' == 'destroy'

Sometimes we might want to create a cluster and then work on
it for debug/further investigation purposes. Let's make sure
we don't reap the resources created if we explicitly asked
for them to be preserved (the default is to reap resources,
though).

Signed-off-by: Lucas Meneghel Rodrigues <8ad3460456640ab580599f5440c5a8d925a620b9@scylladb.com>

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