Add network bonding collector

This collector exposes two metrics:

- net_bonding_slaves: configured slaves per bonding interface
- net_bonding_slaves_active: currently active slaves per bonding
  interface

collector/bonding_test.go

@@ -0,0 +1,23 @@
+package collector
+
+import (
+	"testing"
+)
+
+func TestBonding(t *testing.T) {
+	bondingStats, err := readBondingStats("fixtures/bonding")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if bondingStats["bond0"][0] != 0 || bondingStats["bond0"][1] != 0 {
+		t.Fatal("bond0 in unexpected state")
+	}
+
+	t.Logf("int: %v", bondingStats["int"])
+	if bondingStats["int"][0] != 2 || bondingStats["int"][1] != 1 {
+		t.Fatal("int in unexpected state")
+	}
+	if bondingStats["dmz"][0] != 2 || bondingStats["dmz"][1] != 2 {
+		t.Fatal("dmz in unexpected state")
+	}
+}