desiredRange for PortManager::reserve_port

Client can ask `PortManager::reserve_port` to allocate in desired (specific) range to test or avoid some specific cases.

For example, some servers can work only with ports less than 32768.

I offer to append the new argument 'desiredRange' to PortManager::reserve_port to provide this feature:

``` python
PortManager::reserve_port(desiredRange: range = None)
```