More specific idb failure logging

Summary: The "Conflict in temp dir" message was misleading when there were 0, rather than >1 file. This fixes that error message.

Reviewed By: passy

Differential Revision: D15716247

fbshipit-source-id: 572addf99f623cdcffd7602dd3935bb69a50d047

src/utils/CertificateProvider.js

@@ -362,9 +362,12 @@ export default class CertificateProvider {
       .then(dir => {
         return promisify(fs.readdir)(dir)
           .then(items => {
-            if (items.length !== 1) {
+            if (items.length > 1) {
               throw new Error('Conflict in temp dir');
             }
+            if (items.length === 0) {
+              throw new Error('Failed to pull CSR from device');
+            }
             return items[0];
           })
           .then(fileName => {