s2i native image builder doesn't respect a project's gradle wrapper nor any overridden project settings

[edeandrea]

The assemble script in the quarkus-native-binary-s2i-scripts module don't respect a project's Gradle wrapper

if "$USE_GRADLE"; then
  BUILD_DIR=build
  mkdir -p build/libs
  gradle buildNative --docker-build=false

This script always assumes that a build's output directory is build and uses the gradle script instead of the gradlew script. By not using gradlew, the image forces the build to a particular Gradle version instead of using the version that the project itself is declaring should be used. In addition a particular build may have changed the $buildDir property, in which case the build directory won't exist and output will be elsewhere.