Terminate immediately on a failure (any_errors_fatal)

This commit implements the ability to terminate the entire execution immediately when one of the hosts has failed, unlike the default behavior where the execution continues on the other hosts.

This can be done by setting `any_errors_fatal` property of a playbook or a specific task.

```yaml
- name: My playbook
  hosts: all
  any_errors_fatal: True

  tasks:
  - file: path=/bin/bash state=file
    any_errors_fatal: False
  - shell: "[ `hostname` = centos1 ]"
  - shell: ls
```

I'm not sure if you want this feature, but it was previously discussed on the following thread:
https://groups.google.com/forum/#!msg/ansible-project/1bCSwQR7tQ4/jSjXoGEb3hMJ

Please take a look, thanks.