Enable no-floating-promises tslint rule (#626)

This prevents the code from getting promises and not handling them
appropriately, a known source of subtle bugs and race conditions.

packages/aws-cdk/test/test.account-cache.ts

@@ -4,18 +4,18 @@ import path = require('path');
 import { AccountAccessKeyCache } from '../lib/api/util/account-cache';
 
 export = {
-    'setUp'(cb: ICallbackFunction) {
+    async 'setUp'(cb: ICallbackFunction) {
         const self = this as any;
-        fs.mkdtemp('/tmp/account-cache-test').then(dir => {
-            self.file = path.join(dir, 'cache.json');
-            self.cache = new AccountAccessKeyCache(self.file);
-            return cb();
-        });
+        const dir = await fs.mkdtemp('/tmp/account-cache-test');
+        self.file = path.join(dir, 'cache.json');
+        self.cache = new AccountAccessKeyCache(self.file);
+        return cb();
     },
 
-    'tearDown'(cb: ICallbackFunction) {
+    async 'tearDown'(cb: ICallbackFunction) {
         const self = this as any;
-        fs.remove(path.dirname(self.file)).then(cb);
+        await fs.remove(path.dirname(self.file));
+        cb();
     },
 
     async 'get(k) when cache is empty'(test: Test) {

packages/simple-resource-bundler/bin/bundler.ts

@@ -38,7 +38,7 @@ async function main() {
             'export = resources;'
         ];
 
-        fs.writeFile(path.join(output, 'resources.d.ts'), declContents.join('\n'));
+        await fs.writeFile(path.join(output, 'resources.d.ts'), declContents.join('\n'));
     }
 }
 

tools/cdk-build-tools/bin/cdk-package.ts

@@ -47,7 +47,7 @@ async function main() {
         await fs.move(tarball, path.join(target, path.basename(tarball)));
     }
 
-    detector.markClean();
+    await detector.markClean();
 }
 
 main().then(() => {

tslint.yaml

@@ -45,3 +45,6 @@ rules:
 
     # Without this rule, _blabla would be disallowed, which is necessary to silence unused variable errors.
     variable-name: [true, "ban-keywords", "check-format", "allow-leading-underscore"]
+
+    # Unhandled promises are the source of all kinds of bugs and race conditions...
+    no-floating-promises: true