Dorian/checkprocess

Add service check for the process check.
Could you use a dictionary instead ? It would be more explicit than relying on the value of AgentCheck.OK and other statuses (that could change).

you should do something like 
```python
status_str = {
    AgentCheck.OK: 'ok',
    AgentCheck.WARNING: 'warning', 
    AgentCheck.CRITICAL: 'critical'
}