tools: add download testing

This script will take an environment variable (NODE_VERSION) and
download all of the files from `http://nodejs.org/dist/v<NODE_VERSION>/`
It will then loop through the `SHASUMS256.txt` file to check if the
SHA256SUMS match up. Initial issue here:
#513

tools/download-test.sh

@@ -0,0 +1,59 @@
+#!/bin/bash
+
+while [[ $# -gt 1 ]]
+do
+  key="$1"
+
+  case "$key" in
+      -t|--tap)
+      TAP="$2"
+      shift # past argument
+      ;;
+      *) # unknown option
+      ;;
+  esac
+  shift # past argument or value
+done
+
+if [ "$DOWNLOAD_LOCATION" == "Nightly" ]; then
+	DOWNLOAD_DIR="nightly"
+else
+	DOWNLOAD_DIR="release"
+fi
+
+LINK=`rsync rsync://unencrypted.nodejs.org/nodejs/$DOWNLOAD_DIR/ | grep $NODE_VERSION | sort -t. -k 1,1n -k 2,2n -k 3,3n | tail -1 | awk '{print $5}'`
+
+if [ -z "$NODE_VERSION" ]; then
+  echo "NODE_VERSION is undefined! Please declare NODE_VERSION"
+  exit 1
+fi
+
+# Remove old files
+[ "$TAP" ] && rm -rf "$TAP"
+rm -rf v*
+
+# Scrape the download server
+rsync -av rsync://unencrypted.nodejs.org/nodejs/"$DOWNLOAD_DIR"/"$LINK" .
+
+num=1
+cat "$LINK"/SHASUMS256.txt | { while read line
+do
+   sha=$(echo "${line}" | awk '{print $1}')
+   file=$(echo "${line}" | awk '{print $2}')
+   echo "Checking shasum for $file"
+   remoteSHA=$(shasum -a 256 "$LINK/$file" | awk '{print $1}')
+   if [ "$remoteSHA" != "$sha" ]; then
+     echo "Error - SHASUMS256 does not match for $file"
+     echo "Expected - $sha"
+     echo "Found - $remoteSHA"
+     [ "${TAP}" ] && echo "not ok $num SHASUMS256 does not match for $file" >> "$TAP"
+     return 1
+   else
+     echo "Pass - SHASUMS256 for $file is correct"
+     [ "$TAP" ] && echo "ok $num SHASUMS256 for $file is correct" >> "$TAP"
+   fi
+   let num++
+done
+let num--
+[ "$TAP" ] && echo "1..$num" >> "$TAP"
+}