pause plugin doesn't flush raw_input prompt

##### Issue Type:

Bugfix Pull Request

##### Ansible Version:

ansible 1.4.3

##### Environment:

N/A

##### Summary:

We are using a wrapper python script to run ansible-playbook. We use subprocess to execute and print the stdout as and when its written. Problem is when we use pause it doesn't display the prompt string as raw_input does not flush stdout before reading from stdin.

It looks like a dirty fix to add "\n" to the prompt string but i don't see any other way to over come this. If anyone else have a better fix please do propose/suggest.

##### Steps To Reproduce:

```yaml
#File: test_play.yml
- name: Test
  hosts: $nodes
  gather_facts: false

  tasks:
    - name: Waiting for User
      local_action: pause prompt="Do you want to continue (yes/no)? "
```

```python
#!/usr/bin/env python
#File: test.py
import shlex, subprocess

def run_process(process):
    process = process.encode("utf-8")
    command = shlex.split(process)
    p = subprocess.Popen(command, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
    for line in iter(p.stdout.readline, b''):
        print line,

cmd = "/usr/bin/python -u /usr/bin/ansible-playbook -i hosts.txt test_play.yml -e 'nodes=local'"
run_process(cmd)
```

```
shell $ python test.py
```

##### Expected Results:
```
PLAY [Test] *******************************************************************

TASK: [Waiting for User] ******************************************************
[localhost]
Do you want to continue (yes/no)? :
```

##### Actual Results:
```
PLAY [Test] *******************************************************************

TASK: [Waiting for User] ******************************************************
[localhost]
```
Merge pull request #6217 from ashokrajar/patch-1

pause plugin doesn't flush raw_input prompt