[pycue] Proc type uses wrong attribute for booked_time

**Describe the bug**

The api wrapper proc.py implements a function bookedTime that fails with AttributeError.

**To Reproduce**

```python
     host = opencue.api.findHost("<host>")
     procs = host.getProcs()
     proc = procs[0]              # type(proc) == opencue.wrappers.proc.Proc
     proc.bookedTime()            # AttributeError: 'Proc' object has no attribute 'booked_time'
```
