Remove validation for Capacity as it got moved from Spec to Status.

Also fix breakage from ExternalID validation: Default ExternalID to node name when not specified.

pkg/api/testing/fuzzer.go

@@ -230,6 +230,10 @@ func FuzzerFor(t *testing.T, version string, src rand.Source) *fuzz.Fuzzer {
 				}
 			}
 		},
+		func(n *api.Node, c fuzz.Continue) {
+			c.FuzzNoCustom(n)
+			n.Spec.ExternalID = "external"
+		},
 	)
 	return f
 }