Currently generated zaqar.conf.sample is missing oslo.cache library
options, but they are used by Zaqar and are important in production
install.
This patch makes the command 'tox -e gencofig' generate also oslo.cache
options.
Change-Id: Ia8f78fd5a106888882f882aed8d8355e7e1e459e
Closes-Bug: 1560707
96717386a5