scripts: build-release -> build-binary

This makes the functionality of the script more clear, and always use
bash to run the script because it has bash-specific grammar.

scripts/build-release → scripts/build-binary

@@ -1,4 +1,6 @@
-#!/bin/sh -e
+#!/usr/bin/env bash
+
+set -e
 
 VER=$1
 PROJ="etcd"