name ec2 instances and security groups consistently

Security groups created by `spark-ec2` do not prepend “spark-“ to the
name.

Since naming the instances themselves is new to `spark-ec2`, it’s better
to change that pattern to match the existing naming pattern for the
security groups, rather than the other way around.

Author: Nicholas Chammas <nicholas.chammas@gmail.com>
Author: nchammas <nicholas.chammas@gmail.com>

Closes #1344 from nchammas/master and squashes the following commits:

f7e4581 [Nicholas Chammas] unrelated pep8 fix
a36eed0 [Nicholas Chammas] name ec2 instances and security groups consistently
de7292a [nchammas] Merge pull request #4 from apache/master
2e4fe00 [nchammas] Merge pull request #3 from apache/master
89fde08 [nchammas] Merge pull request #2 from apache/master
69f6e22 [Nicholas Chammas] PEP8 fixes
2627247 [Nicholas Chammas] broke up lines before they hit 100 chars
6544b7e [Nicholas Chammas] [SPARK-2065] give launched instances names
69da6cf [nchammas] Merge pull request #1 from apache/master

ec2/spark_ec2.py

@@ -428,11 +428,11 @@ def launch_cluster(conn, opts, cluster_name):
     for master in master_nodes:
         master.add_tag(
             key='Name',
-            value='spark-{cn}-master-{iid}'.format(cn=cluster_name, iid=master.id))
+            value='{cn}-master-{iid}'.format(cn=cluster_name, iid=master.id))
     for slave in slave_nodes:
         slave.add_tag(
             key='Name',
-            value='spark-{cn}-slave-{iid}'.format(cn=cluster_name, iid=slave.id))
+            value='{cn}-slave-{iid}'.format(cn=cluster_name, iid=slave.id))
 
     # Return all the instances
     return (master_nodes, slave_nodes)
@@ -699,6 +699,7 @@ def ssh(host, opts, command):
             time.sleep(30)
             tries = tries + 1
 
+
 # Backported from Python 2.7 for compatiblity with 2.6 (See SPARK-1990)
 def _check_output(*popenargs, **kwargs):
     if 'stdout' in kwargs: