Unfortunately, newer versions of protobuf check that the file suffix ends
in _pb2.py:

sudo ./zdtm.py run -t zdtm/static/apparmor_stacking
Traceback (most recent call last):
  File "./zdtm.py", line 23, in <module>
    import criu as crpc
  File "/home/ubuntu/criu/test/criu.py", line 12, in <module>
    import rpc
  File "/home/ubuntu/criu/test/rpc.py", line 36, in <module>
    type=None),
  File "/usr/lib/python2.7/dist-packages/google/protobuf/descriptor.py", line 652, in __new__
    _message.Message._CheckCalledFromGeneratedFile()
TypeError: Descriptors should not be created directly, but only retrieved from their parent.

v2: fix up the clean target, and remove some comments that were about the
    old rename
Signed-off-by: Tycho Andersen <tycho.andersen@canonical.com>
CC: Laurent Dufour <ldufour@linux.vnet.ibm.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>