Use oslo.config generator in murano

Similarly with the way it was done in the murano-agent, added
the ability to use the oslo-config-generator for creating a sample
configuration file murano.conf.sample.

Now to create the file, you must run:
tox -egenconfig

Change-Id: I8b06336d75eccfd598ce9033333884f75f393a09
Merge "Use oslo.config generator in murano"