GCE: Allow nodes to exceed target pool maximums

If we would exceeded the TargetPool API maximums, instead just
randomly select some subsection of the nodes to include in the TP
instead.

pkg/util/rand/rand_test.go

@@ -18,6 +18,8 @@ package rand
 
 import (
 	"math/rand"
+	"reflect"
+	"sort"
 	"strings"
 	"testing"
 )
@@ -71,3 +73,14 @@ func TestPerm(t *testing.T) {
 		}
 	}
 }
+
+func TestShuffle(t *testing.T) {
+	Seed(5) // Arbitrary RNG seed for deterministic testing.
+	have := []int{0, 1, 2, 3, 4}
+	want := []int{3, 2, 4, 1, 0} // "have" shuffled, with RNG at Seed(5).
+	got := append([]int{}, have...)
+	Shuffle(sort.IntSlice(got))
+	if !reflect.DeepEqual(got, want) {
+		t.Errorf("Shuffle(%v) => %v, want %v", have, got, want)
+	}
+}