Change NetConnectNotAllowedError to inherit from Exception

Because a default ruby rescue block:
```
begin
rescue
end
```
will catch StandardErrors, all NetConnectNotAllowedErrors will be swallowed by the block above. So they wont raise in your test suite. We now changed the parent from StandardError to Exception to allow it to bubble up into our test suite. 

We also renamed the class to NetConnectNotAllowedException to reflect this change.