fakevm: switch config library to oslo.config
fakevm: update fakevm plugins

- switch config library to oslo.config
- fix some bugs
add comment to rootwrap.d/fakevm.filters
fakevm: use vif wrapper

fakevm_agent:
  - switch config library to oslo.config
  - use vif wrapper instead of nova vif driver

vif.py:
  - to be executable without quantum-fakevm-vif-wrapper