CLI debug mode improvements

If `--debug` mode is used, cURL request line and raw response body will also be printed the console.

```
(virtualenv)vagrant@vagrant-ubuntu-trusty-64:/data/stanley$ python ./st2client/st2client/shell.py --debug execution list
# -------- begin 140434055391696 request ----------
curl -X GET -H  'Connection: keep-alive' -H  'Accept-Encoding: gzip, deflate' -H  'Accept: */*' -H  'User-Agent: python-requests/2.5.0 CPython/2.7.6 Linux/3.13.0-36-generic' 'http://localhost:9101/v1/actionexecutions/?limit=50'
# -------- begin 140434055391696 response ----------
[
    {
        "status": "succeeded", 
        "start_timestamp": "2014-12-08T20:55:48.021000Z", 
        "parameters": {
            "cmd": "date"
        }, 
        "callback": {}, 
        "result": {
            "localhost": {
                "succeeded": true, 
                "failed": false, 
                "return_code": 0, 
                "stderr": "", 
                "stdout": "Mon Dec  8 20:56:29 UTC 2014"
            }
        }, 
        "context": {
            "user": "stanley"
        }, 
        "action": "core.local", 
        "id": "548610540640fd2ca3c1eb71", 
        "end_timestamp": "2014-12-08T20:56:29.401000Z"
    }, 
    {
        "status": "succeeded", 
        "start_timestamp": "2014-12-08T20:55:22.204000Z", 
        "parameters": {
            "cmd": "date"
        }, 
        "callback": {}, 
        "result": {
            "localhost": {
                "succeeded": true, 
                "failed": false, 
                "return_code": 0, 
                "stderr": "", 
                "stdout": "Mon Dec  8 20:55:25 UTC 2014"
            }
        }, 
        "context": {
            "user": "stanley"
        }, 
        "action": "core.local", 
        "id": "5486103a0640fd2ca3c1eb70", 
        "end_timestamp": "2014-12-08T20:55:25.792000Z"
    }
]
# -------- end 140434055391696 response ------------

+--------------------------+------------+--------------+-----------+------------------------------+------------------------------+
| id                       | action     | context.user | status    | start_timestamp              | end_timestamp                |
+--------------------------+------------+--------------+-----------+------------------------------+------------------------------+
| 5486103a0640fd2ca3c1eb70 | core.local | stanley      | succeeded | Mon, 08 Dec 2014 20:55:22    | Mon, 08 Dec 2014 20:55:25    |
|                          |            |              |           | UTC                          | UTC                          |
| 548610540640fd2ca3c1eb71 | core.local | stanley      | succeeded | Mon, 08 Dec 2014 20:55:48    | Mon, 08 Dec 2014 20:56:29    |
|                          |            |              |           | UTC                          | UTC                          |
+--------------------------+------------+--------------+-----------+------------------------------+------------------------------+
```