Let's just rely on brooklyn.properties, which should be parsed automatically. That's how `AbstractJcloudsLocationTest` works (although that class may well not be the best to copy the pattern of!).

It does stuff like (but we want Java rather than Groovy):

        ctx = Entities.newManagementContext(ImmutableMap.of("provider", provider));
        loc = ctx.getLocationRegistry().resolve(provider + (regionName == null ? "" : ":" + regionName));
        SshMachineLocation machine = obtainMachine([imageId:imageId, imageOwner:imageOwner])

But that presumably requires implementing the EnstratiusResolver's string parsing methods.