Returns last known GRR version that the client used.

def GetClientVersion(client_id, token=None):
  """Returns last known GRR version that the client used."""
  if data_store.RelationalDBEnabled():
    sinfo = data_store.REL_DB.ReadClientStartupInfo(client_id=client_id)
    if sinfo is not None:
      return sinfo.client_info.client_version
    else:
      return config.CONFIG["Source.version_numeric"]
  else:
    with aff4.FACTORY.Open(client_id, token=token) as client:
      cinfo = client.Get(client.Schema.CLIENT_INFO)
      if cinfo is not None:
        return cinfo.client_version
      else:
        return config.CONFIG["Source.version_numeric"]