Standardize example role definitions

Standardize example role definitions

As we create new standard roles, we should include them from a single
location for ease of use and to reduce the duplication of the role
definitions elsewhere. This change adds a roles folder to the THT that
can be used with the new roles commands in python-tripleoclient by the
end user to generate a roles_data.yaml from a standard set of roles.

Depends-On: I326bae5bdee088e03aa89128d253612ef89e5c0c
Change-Id: Iad3e9b215c6f21ba761c8360bb7ed531e34520e6
Related-Blueprint: example-custom-role-environments