The BlueStore.cc stuff had gone into the libos target at some point, but not all the things (especially rocksdb) that it depends on.

This is a fairly crude fix that just goes ahead and pulls in everything without any fancy dependency checking. Building rocksdb with the same command line as in autotools: cmake's ExternalProject might e a slicker option but unclear if it adds much when we already have a one-liner for building the external project.