Fix root project dependencies in build file.
requested to merge stfs/java-gradle-multimodules:stfs-13075-patch-gradle-build-file into 13075-add-gradle-project
As per the discussion in gitlab-org/gitlab#13075 (comment 251940015) there was a problem with dependencies not being reported for the root project in multi-project Gradle builds.
After investigation it turns out that the Gradle test project was not defined to have any dependencies, but rather, the dependencies were inside the subprojects block. This MR modifies the root project build file so that dependencies are defined on the root project itself.