Target definitions should only access a single VIATRA repository

By using a version-specific repository declaration in the target files, target platform resolution will become faster as fewer repositories need to be consulted.

Signed-off-by: Zoltan Ujhelyi <zoltan.ujhelyi@incquerylabs.com>
Change-Id: I4421060bbf0e2c1aab6a96a2db6556efe21eb6fd