Move more responsibility to common EC2 module

Moved `AWS_REGIONS` into `ec2` module
Created `ec2_connect` method in `ec2` module
Updated modules able to use `ec2_connect` and `AWS_REGIONS`

library/cloud/elasticache

@@ -137,15 +137,6 @@ import sys
 import os
 import time
 
-AWS_REGIONS = ['ap-northeast-1',
-               'ap-southeast-1',
-               'ap-southeast-2',
-               'eu-west-1',
-               'sa-east-1',
-               'us-east-1',
-               'us-west-1',
-               'us-west-2']
-
 try:
     import boto
     from boto.elasticache.layer1 import ElastiCacheConnection