[FEATURE] Clearer default group / role implementations

[mcanoy]

Is your feature request related to a problem? Please describe.
This may be a bug depending on your expectations.

Scenario:

• use default groups-role mappings
• do not add those groups to openshift
• login with valid openshift user

Expectation

• The user is not in a predefined role so the user should be denied access.

Actual

• The user is add to the sonar-users group and allow to view projects

Describe the solution you'd like

I'm not against this behavior but I think the plugin should support a no group then no role implementation and that this new behavior should be the default

Describe alternatives you've considered
meh

Additional context
meh