Use common code for ec2_elb and ec2_elb_lb

Uses the new get_aws_connection_info
and connect_to_aws common methods to reuse code

Now complains if region is not set in one of the
three possible methods

Also moved over to common documentation code so
this is actually based on #6913
Merge pull request #6914 from willthames/elb_redo

Use common code for ec2_elb and ec2_elb_lb