`dl_deps.sh` can download the same dependency in several versions but unpacks them into the same directory

This issue appeared in the default:latest dependency set where rocksdb and rocksdb:experimental is downloaded but unpacked in the rocksdb directory.

Since downloading is parallel, it could be either of both versions or mixed if they are unpacked together, which may lead to compilation errors.

Expected behavior: Since a ordering in the profiles can be given, multiple versions should still be able to download (to separate directories). Each can then be chosen later in compile_deps.sh with -d. Otherwise

Linked to #176 (closed)