EC2 ELB management

This module handles AWS EC2 ELB registration.

* De-registration requires the instance id which can be looked up using
  the ec2_facts module.
* Registration requires both the instance id and the elbs that the
  instance belongs to.

De-registration will return an ec2_elb fact that can be used for
registration in post_tasks.

Example:

```
# basic pre_task and post_task example
pre_tasks:
  - name: Gathering ec2 facts
    ec2_facts:
  - name: Instance De-register
    local_action: ec2_elb
    args:
      instance_id: "{{ ansible_ec2_instance_id }}"
      state: 'absent'
roles:
  - myrole
post_tasks:
  - name: Instance Register
    local_action: ec2_elb
    args:
      instance_id: "{{ ansible_ec2_instance_id }}"
      ec2_elbs: "{{ ec2_elbs }}"
      state: 'present'
```