sdcm.cluster.Node: Make .wait_until_running safer
sdcm.cluster.Node: Make .wait_until_running safer

Since AWS adopts an eventual consistency model, sometimes the method
wait_until_running will raise a botocore.exceptions.WaiterError saying
the instance does not exist. AWS API guide [1] recommends that the
procedure is retried using an exponencial backoff algorithm [2].

[1] http://docs.aws.amazon.com/AWSEC2/latest/APIReference/query-api-troubleshooting.html#eventual-consistency
[2] http://docs.aws.amazon.com/general/latest/gr/api-retries.html

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

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