[v2] remove unnecessary json lists from param values

[mimir-d]

Currently, all of the parameters are expected to be lists, even when it is unnecessary (like the "binary" below).

{
    "name": "gathercmd",
    "label": "make_logdirs",
    "parameters": {
        "binary": ["mkdir"], <--
        "args": ["-p", "/tmp/control_logs"]
    }
}

There is also some api supporting this Param.GetOne. This should be removed, and the descriptors updated to have single values. Proposal

{
    "name": "gathercmd",
    "label": "make_logdirs",
    "parameters": {
        "binary": "mkdir", <--
        "args": ["-p", "/tmp/control_logs"]
    }
}