buildbox-casd and buildbox-fuse mismatch when having both wheel and system installed versions

[abderrahim]

When having buildbox installed in the PATH and in the wheel, buildstream mismatches them. IIRC, it will use the buildbox-casd from the PATH and buildbox-fuse from the wheel.

If the two versions are incompatible, this can result in a buildstream crash with the error:

    grpc._channel._MultiThreadedRendezvous: <_MultiThreadedRendezvous of RPC that terminated with:
        status = StatusCode.INTERNAL
        details = "std::runtime_error exception thrown at [buildboxcasd_fusestager.cpp:144], errMsg = "The FUSE stager child process unexpectedly died with exit code 1""
        debug_error_string = "UNKNOWN:Error received from peer  {created_time:"2024-11-20T09:16:31.255363002+00:00", grpc_status:13, grpc_message:"std::runtime_error exception thrown at [buildboxcasd_fusestager.cpp:144], errMsg = \"The FUSE stager child process unexpectedly died with exit code 1\""}"