cmd/dlv: fix exit status for trace subcommand (#3263)

We currently return an error when the command exits because a process
exited error is always returned. Detect this like we do in other code
paths to return a 0 exit code instead of nonzero which indicates the
command itself failed and can confuse other tools.

cmd/dlv/cmds/commands.go

@@ -732,7 +732,9 @@ func traceCmd(cmd *cobra.Command, args []string) {
 		err = cmds.Call("continue", t)
 		if err != nil {
 			fmt.Fprintln(os.Stderr, err)
-			return 1
+			if !strings.Contains(err.Error(), "exited") {
+				return 1
+			}
 		}
 		return 0
 	}()

cmd/dlv/dlv_test.go

@@ -1038,7 +1038,7 @@ func TestTrace2(t *testing.T) {
 	if !bytes.Contains(output, expected) {
 		t.Fatalf("expected:\n%s\ngot:\n%s", string(expected), string(output))
 	}
-	cmd.Wait()
+	assertNoError(cmd.Wait(), t, "cmd.Wait()")
 }
 
 func TestTraceMultipleGoroutines(t *testing.T) {