Add functional testing README
Add functional testing README

Outline the background and goal of the functional testing.  Want to make
sure there is consensus on how this should look. Next step is to
reorganize the functional tests to follow the plan outlined here.

Change-Id: I1d6889682f50f78b0681c99b77475adba95ef807

CCI-MOC/python-novaclient,mat128/python-novaclient,takeshineshiro/python-novaclient,CCI-MOC/python-novaclient,guptaankita/python-novaclient,guptaankita/python-novaclient,mat128/python-novaclient,takeshineshiro/python-novaclient