seat: a push to a named machine waits for the machine's answer, so its call says how it went (issue 629)

The seat ran `push <node> --wait 0`, so a push's call ended at "sent" and nobody learned whether the machine applied it. The caller is answered before a push starts (answersFirst, issue 265), so waiting holds nobody: the call now waits up to two minutes for the machine's own report and keeps it, applied, refused with the machine's reason, or each failed resource with its error.

cmd/mesh-controller/push.go

@@ -740,7 +740,14 @@ func waitForApplied(ctx context.Context, inv *inventory.Inventory, node, digest
 				fmt.Printf("%s applied it\n", node)
 				return nil
 			case inventory.OutcomeFailed:
-				return fmt.Errorf("%s applied what it was sent but %d resource(s) failed", node, len(doing.Failed))
+				// Each failed resource by id with the machine's own words, so the answer says what to fix
+				// without a second look (novox/hq issue 629).
+				var each []string
+				for _, f := range doing.Failed {
+					each = append(each, f.ID+": "+f.Error)
+				}
+				return fmt.Errorf("%s applied what it was sent but %d resource(s) failed: %s", node, len(doing.Failed),
+					strings.Join(each, "; "))
 			case inventory.OutcomeRefused:
 				return fmt.Errorf("%s refused what it was sent: %s", node, doing.Refused)
 			}