non-root-installer add a flag which lists all the supported versions

What's the issue?
At the moment, user have no way of determining which versions are supported for the non-root-installer; they should be able to determine (up-front) if the upgrade path they have is supported or not.

What's the fix?
Add a flag called '--list-versions' which lists the supported versions, we should use x in the place of patch releases to avoid having to update this list every time a new version is released.

./cb-non-root-installer --list-versions

6.0.x

6.5.x

6.6.x

7.0.x

7.1.x