[SPARK-4983] Insert waiting time before tagging EC2 instances

The boto API doesn't support tag EC2 instances in the same call that launches them.
We add a five-second wait so EC2 has enough time to propagate the information so that
the tagging can succeed.

Author: GenTang <gen.tang86@gmail.com>
Author: Gen TANG <gen.tang86@gmail.com>

Closes #3986 from GenTang/spark-4983 and squashes the following commits:

13e257d [Gen TANG] modification of comments
47f0675 [GenTang] print the information
ab7a931 [GenTang] solve the issus spark-4983 by inserting waiting time
3179737 [GenTang] Revert "handling exceptions about adding tags to ec2"
6a8b53b [GenTang] Revert "the improvement of exception handling"
13e97a6 [GenTang] Revert "typo"
63fd360 [GenTang] typo
692fc2b [GenTang] the improvement of exception handling
6adcf6d [GenTang] handling exceptions about adding tags to ec2

(cherry picked from commit 0f3a360)
Signed-off-by: Josh Rosen <joshrosen@databricks.com>

ec2/spark_ec2.py

@@ -480,6 +480,9 @@ def launch_cluster(conn, opts, cluster_name):
         master_nodes = master_res.instances
         print "Launched master in %s, regid = %s" % (zone, master_res.id)
 
+    # This wait time corresponds to SPARK-4983
+    print "Waiting for AWS to propagate instance metadata..."
+    time.sleep(5)
     # Give the instances descriptive names
     for master in master_nodes:
         master.add_tag(