Simple range check on user supplied Containerizer Memory

  // Create a fresh set of resources only for memory.
  // You may want to include all other resources in this set as well.... YMMV!
  Resources rangedResources;

  // Memory resource.
  if (!resources.mem().isSome()) {
    // No memory specified so probe OS or resort to DEFAULT_MEM.
    Bytes mem;
    Try<os::Memory> mem_ = os::memory();
    if (mem_.isError()) {
      LOG(WARNING) << "Failed to auto-detect the size of main memory: '"
                    << mem_.error()
                    << "' ; defaulting to DEFAULT_MEM";
      mem = DEFAULT_MEM;
    } else {
      mem = mem_.get().total;

      // Leave 1 GB free if we have more than 1 GB, otherwise, use all!
      // TODO(benh): Have better default scheme (e.g., % of mem not greater
      // than 1 GB?)
      if (mem > Gigabytes(1)) {
        mem = mem - Gigabytes(1);
      }
    }

    rangedResources += Resources::parse(
        "mem",
        stringify(mem.megabytes()),
        flags.default_role).get();

  } else {
    // Fetch the user supplied memory value from our collection.
    Bytes mem = resource.mem.get();

    // Do a range check on the user supplied values.
    if (mem < SOME_VALUE_YOU_FIND_GOOD_ENOUGH_FOR_A_MINIMUM) {
      LOG(INFO) << "Given memory value is too low, adapting towards minimum.";
      mem = SOME_VALUE_YOU_FIND_GOOD_ENOUGH_FOR_A_MINIMUM;
    } else if (mem > SOME_VALUE_YOU_FIND_GOOD_ENOUGH_FOR_A_MAXIMUM) {
      LOG(INFO) << "Given memory value is too high, adapting towards maximum.";
      mem = SOME_VALUE_YOU_FIND_GOOD_ENOUGH_FOR_A_MAXIMUM;
    }

    // Write possibly adapted resource memory entry back to our resources collection.
    rangedResources += Resources::parse(
        "mem",
        stringify(mem.megabytes()),
        flags.default_role).get();
  }
  
  // You now have a set of range checked resource (rangedResources) for the resource "mem".
  // YEEEHAAAW!