PortAllocator: Base64 encode secrets

Random list of bytes does not transmit well over JSON

Change-Id: I3f0a68fed668e91960ef68ca02d87f61f8de154c
diff --git a/core/port-allocator/main.go b/core/port-allocator/main.go
index 3d69ab9..6c7d361 100644
--- a/core/port-allocator/main.go
+++ b/core/port-allocator/main.go
@@ -2,6 +2,7 @@
 
 import (
 	"crypto/rand"
+	"encoding/base64"
 	"encoding/json"
 	"flag"
 	"fmt"
@@ -376,7 +377,7 @@
 	if err != nil {
 		return "", fmt.Errorf("error generating secret: %v", err)
 	}
-	return string(b), nil
+	return base64.StdEncoding.EncodeToString(b), nil
 }
 
 func main() {