Update readme with list of supported volume drivers

Change-Id: I718221bb8092843c014d48f2124bb4432f7f939a
Closes-bug: #1273504
use new python_packages attributes from -common

*_python_packages attributes are being moved to -common in order to
remove the duplication from all the cookbooks which are using them

Change-Id: I60798fb39f6167eafd0cc483dca9bb930a236946
Implements: blueprint move-python-db-client-attrs-to-common