Revert "Remove linear backoff."

This reverts commit adb4eaa and
increases the wait interval to 5 seconds.

ec2/spark_ec2.py

@@ -669,8 +669,11 @@ def wait_for_cluster_state(conn, opts, cluster_instances, cluster_state):
 
     start_time = datetime.now()
 
+    num_attempts = 0
+    conn = ec2.connect_to_region(opts.region)
+
     while True:
-        time.sleep(5)  # seconds
+        time.sleep(5 * num_attempts)  # seconds
 
         for i in cluster_instances:
             i.update()
@@ -687,13 +690,14 @@ def wait_for_cluster_state(conn, opts, cluster_instances, cluster_state):
             if all(i.state == cluster_state for i in cluster_instances):
                 break
 
+        num_attempts += 1
+
         sys.stdout.write(".")
         sys.stdout.flush()
 
     sys.stdout.write("\n")
 
     end_time = datetime.now()
-
     print "Cluster is now in '{s}' state. Waited {t} seconds.".format(
         s=cluster_state,
         t=(end_time - start_time).seconds