[S2I] Build succeeds even if the git clone has failed

When there are issue with git the build still succeeds
The problem is that S2I script identifies there is no pom then it just skips the building phase and create the container.

I think that the use-cases with S2I without Maven are quite rare so I propose to handle them as an exception and require a env var to be set that Maven build is not required and have build failed in other cases.

An example of log file when this happens is attached