[oe] [meta-python][PATCH]: update some python packages bb

[mingli.yu at windriver.com]

1, 
  Remove pytest for python-mccabe to avoid dependency 
  on python-runner as only one file test_mccabe.py import 
  pytest and this test_mccabe.py file not install on 
  our target eventually.

2, Add python-pbr bb file as python-mock depends on
  python-pbr-native

3, Add python-pbr-native dependency for python-mock