Define product dependency in module repository

Currently the product dependency (now to fixed qt5.git) branch is resolved either via target branch (Qt version specific) or via the wip/<module>/<branch> branches in qt5.git.

Neither options are really convenient for module maintainer as changing them requires gerrit admin rights. Instead the module should be able the define the dependency in its own repository.

This would allow e.g., non-qmake module to depend on specific qt5 branch for its provisioining. This would also enable making the dependency to HEAD of branch to always use the latest provisioning (and therefore tier2 images), which is not possible with wip branches.