Revisit AeatherGrapeEngineTests

[snicoll]

In the fix for #2947 (b838513) I had to update those tests to include our milestone repo so that Spring Framework 4.2.RC1 is resolved.

Looking at how Maven works, I wonder how it worked before (since it needs a repository source for everything, even if the dependency is cached in the local repository). To me, the current behaviour is more consistent.

ping @wilkinsona

[wilkinsona]

It works with BUILD-SNAPHOT dependencies as, while they're considered unavailable when Central is the only available repository, they're also considered not to be tracked so the availability is overridden to true.