Added ability to start and stop existing EC2 instances.

This adds the ability to set the state of an existing instance to 'started' or 'stopped' in the ec2 module.

Example usage to start an instance:

- name: Start an EC2 instance
  local_action:
    module: ec2
    instance_ids: '{{ instance_ids }}'
    region: '{{ region }}'
    state: running
    wait: True

Since I had this in my main fork I rebased and reset my fork and created a branch to properly put this change in to. So this is the same changes from my original pull #4805.