Race condition with release file creation

The release file is part of all product images in the build. We used to generate it for each image individually, but a while back, we changed to generate it just for the exploded image, and then let jlink use the one as source for generating individually modified release files for each linked image.

The problem is that the release file is still generated in Images.gmk, which is called multiple times. This means each call to this file may try to generate the release file at the same time, which may result in a corrupt release file.

For Oracle builds, we have another image which is currently not correctly depending on the release file being created before linking, which is intermittently failing the build.

The correct solution to all of this is to move the release file generation to separate build step, which is part of creating the exploded image.