rpk cluster logdirs: fix error exit, print by size descending

* if listing topics failed, we would panic
* for printing by size, we should print descending similar to other CLI
  tools

src/go/rpk/pkg/cli/cluster/logdirs.go

@@ -81,9 +81,14 @@ where revision is a Redpanda internal concept.
  if len(topics) > 0 {
  listed, err := adm.ListTopics(context.Background(), topics...)
  out.MaybeDie(err, "unable to describe topics: %v", err)
+ var exit bool
  listed.EachError(func(d kadm.TopicDetail) {
  fmt.Fprintf(os.Stderr, "unable to discover the partitions on topic %q: %v\n", d.Topic, d.Err)
+ exit = true
  })
+ if exit {
+ os.Exit(1)
+ }
  s = listed.TopicsSet()
  }
 
@@ -190,7 +195,7 @@ where revision is a Redpanda internal concept.
  // what we have already ordered and aggregated.
  if sortBySize {
  sort.SliceStable(rows, func(i, j int) bool {
- return rows[i].Size < rows[j].Size
+ return rows[i].Size >= rows[j].Size
  })
  }