Gracefully handle absence fo the ~/.aws/credentials file

The JS SDK assumes the file exists when it is passed as an argument, so
this change makes the CDK Toolkit check for file existence before
passing down to the SDK layer. Additionally, the SDK "ini file"
re-implementation failed to check for file existece before attempting to
load file contents.

Fixes #540

packages/aws-cdk/lib/api/util/sdk.ts

@@ -1,5 +1,6 @@
 import { Environment} from '@aws-cdk/cx-api';
 import AWS = require('aws-sdk');
+import fs = require('fs-extra');
 import os = require('os');
 import path = require('path');
 import { debug } from '../../logging';
@@ -157,7 +158,7 @@ function makeCLICompatibleCredentialProvider(profile: string | undefined) {
     return new AWS.CredentialProviderChain([
         () => new AWS.EnvironmentCredentials('AWS'),
         () => new AWS.EnvironmentCredentials('AMAZON'),
-        () => new AWS.SharedIniFileCredentials({ profile, filename }),
+        ...(fs.pathExistsSync(filename) ? [() => new AWS.SharedIniFileCredentials({ profile, filename })] : []),
         () => {
             // Calling private API
             if ((AWS.ECSCredentials.prototype as any).isConfiguredForEcsCredentials()) {
@@ -200,4 +201,4 @@ function getCLICompatibleDefaultRegion(profile: string | undefined): string | un
     }
 
     return region;
-}
+}

packages/aws-cdk/lib/api/util/sdk_ini_file.ts

@@ -6,6 +6,7 @@
  */
 
 import AWS = require('aws-sdk');
+import fs = require('fs-extra');
 import os = require('os');
 import path = require('path');
 
@@ -44,9 +45,9 @@ export class SharedIniFile {
 
   private ensureFileLoaded() {
     if (!this.parsedContents) {
-      this.parsedContents = (AWS as any).util.ini.parse(
-        (AWS as any).util.readFileSync(this.filename)
-      );
+      this.parsedContents = fs.pathExistsSync(this.filename)
+                          ? (AWS as any).util.ini.parse((AWS as any).util.readFileSync(this.filename))
+                          : {};
     }
   }
-}
+}