Added Cloudwatt driver

Added Driver for new French cloud provider Cloudwatt https://www.cloudwatt.com/fr/

This provider is based on OpenStack but uses a custom kind of authentication,
The request data must look like below:
{'auth': {
  'passwordCredentials': {
    'username': 'THE_USERNAME',
    'password': 'THE_PASSWORD'
  },
  'tenantId': 'THE_TENANT_ID
}}

So, I adapt classes to accept tenant_id argument.

I manually tested it with a custom script and ``Driver.list_nodes()``.
Please use

```python
try:
    import simplejson as json
except ImportError:
    import json
```

Otherwise it won't work with Python 2.5.