Seeds math/rand (#98)

* Seeds math/rand

For background on why this is necessary see:

m-lab/dev-tracker#689

* Changes 'unexpected' to 'unintended' in comment

pusher.go

@@ -5,6 +5,7 @@ import (
 	"flag"
 	"fmt"
 	"log"
+	"math/rand"
 	"os"
 	"os/signal"
 	"path"
@@ -182,6 +183,13 @@ M-Lab uniform naming conventions.
 	// ListenForever loops are still running.
 	wg := sync.WaitGroup{}
 
+	// Seeds math/rand with a unique seed. Without this, rand will return a
+	// predictable pattern of "random" numbers, causing the "memoryless" package
+	// to potentially schedule runs of pusher in unintended ways. For more
+	// background, see this issue:
+	// https://github.com/m-lab/dev-tracker/issues/689
+	rand.Seed(time.Now().UnixNano())
+
 	// Set up pushing for every datatype.
 	for _, datatype := range datatypes {
 		// Set up the upload system.