Use bash instead of sh in self extracting archive

`echo -n` and `read` seems to not work the same on mac

Bug: 130257221
Test: generated an archive using the script and ran the result on linux and mac
Change-Id: I129090ccf50781b748bff9a5c7890824d2670ad4

tools/generate-self-extracting-archive.py

@@ -38,7 +38,7 @@ import sys
 import os
 import zipfile
 
-_HEADER_TEMPLATE = """#!/bin/sh
+_HEADER_TEMPLATE = """#!/bin/bash
 #
 {comment_line}
 #