Generate role files automatically based on user input and eliminating mutually exclusive services from a role

There are many services in TripleO that are conflicting and leads to deployment failure when enabled in the same role. Also users have to specify the whole service class like

- OS::TripleO::Services::OpenDaylightApi
- OS::TripleO::Services::OpenDaylightOvs

for enabling ODL on controller role. This is not a good user experience and prone to human error.

This BP proposes to eliminate these 2 problems by making TripleO generate role file based on the user input and also disable conflicting services.

The user should have to specify to enable ODL and TripleO should then do its magic to generate role file with following content:

- OS::TripleO::Services::OpenDaylightApi
- OS::TripleO::Services::OpenDaylightOvs

and NOT include

OS::TripleO::Services::NeutronOvsAgent
OS::TripleO::Services::OVNDBs
OS::TripleO::Services::OVNController

which are mutually exclusive.