New powny kernel/userspace

PS: Tests failed because the new version of requests/vcrpy contains a bug: https://github.com/kevin1024/vcrpy/issues/94
```
Traceback (most recent call last):
  File "/home/mdevaev/projects/yandex/gns/powny/core/apps/__init__.py", line 137, in run
    self.process()
  File "/home/mdevaev/projects/yandex/gns/powny/core/apps/worker.py", line 94, in process
    self._manage_jobs()
  File "/home/mdevaev/projects/yandex/gns/powny/core/apps/worker.py", line 138, in _manage_jobs
    for (job_id, job_proc) in self._jobs_children.items()[:]:
TypeError: 'dict_items' object is not subscriptable
```