Reproduce potential scenario that could be happening with #321

The basic mechanism is the same as #1514, which is short circuiting
issue.
For maven there’s the second problem of the availability of the
publication date.
Fix maven-metadata publishing.

* Fix logic error in transactional semantics for MavenRepsoitoryResolver
* Add metadata generators into the boot/locator DI thingy for Aether.
* Add a spec test to make sure maven-metadata.xml is created for a new dependency.