Fixes AWS configuration on restore

This change removes environmental inference from the restore script,
restoring the usual credential precedence established in `aws-sdk`.

The default region (Sydney) is preserved for back-compatibility.

lib/dynamo-restore.js

@@ -14,22 +14,28 @@ var readline = require('readline');
 var DYNAMO_CHUNK_SIZE = 25;
 
 function DynamoRestore(options) {
+    var params = {};
     options = options || {};
     options.concurrency = options.concurrency || 200;
     options.minConcurrency = 1;
     options.maxConcurrency = options.concurrency;
     options.readcapacity = options.readcapacity || 5;
     options.writecapacity = options.writecapacity || 0;
     options.stopOnFailure = options.stopOnFailure || false;
-    options.awsKey = options.awsKey || process.env.AWS_ACCESS_KEY_ID;
-    options.awsSecret = options.awsSecret || process.env.AWS_SECRET_ACCESS_KEY;
-    options.awsRegion = options.awsRegion || process.env.AWS_DEFAULT_REGION || 'ap-southeast-2';
 
-    AWS.config.update({
-        accessKeyId: options.awsKey,
-        secretAccessKey: options.awsSecret,
-        region: options.awsRegion
-    });
+    if (options.awsRegion) {
+        params.region = options.awsRegion;
+    }
+    else if (!process.env.AWS_REGION) {
+        params.region = process.env.AWS_DEFAULT_REGION || 'ap-southeast-2';
+    }
+
+    if (options.awsKey && options.awsSecret) {
+        params.accessKeyId = options.awsKey;
+        params.secretAccessKey = options.awsSecret;
+    }
+
+    AWS.config.update(params);
 
     this.options = options;
     this.dynamodb = new AWS.DynamoDB();