Always seed math/rand on consul startup

Required for jitter calcs.  This could be done in consul/agent, but this makes it clear it is done only once process-wide.

lib/rand.go

@@ -0,0 +1,18 @@
+package lib
+
+import (
+	"math/rand"
+	"sync"
+	"time"
+)
+
+var (
+	once sync.Once
+)
+
+// SeedMathRand provides weak, but guaranteed seeding, which is better than
+// running with Go's default seed of 1.  A call to SeedMathRand() is expected
+// to be called via init(), but never a second time.
+func SeedMathRand() {
+	once.Do(func() { rand.Seed(time.Now().UTC().UnixNano()) })
+}

main.go

@@ -6,8 +6,14 @@ import (
 	"io/ioutil"
 	"log"
 	"os"
+
+	"github.com/hashicorp/consul/lib"
 )
 
+func init() {
+	lib.SeedMathRand()
+}
+
 func main() {
 	os.Exit(realMain())
 }