Fix bug in Discover no results screen caused by shard failure reason property being an object (#21601)

src/core_plugins/kibana/public/discover/directives/__snapshots__/no_results.test.js.snap

@@ -333,7 +333,7 @@ Array [
               <code
                 class="euiCodeBlock__code"
               >
-                Awful error
+                {"reason":"Awful error"}
               </code>
             </pre>
           </div>
@@ -362,7 +362,7 @@ Array [
               <code
                 class="euiCodeBlock__code"
               >
-                Bad error
+                {"reason":"Bad error"}
               </code>
             </pre>
           </div>

src/core_plugins/kibana/public/discover/directives/no_results.js

@@ -67,7 +67,7 @@ export class DiscoverNoResults extends Component {
           <EuiSpacer size="s" />
 
           <EuiCodeBlock paddingSize="s">
-            {failure.reason}
+            {JSON.stringify(failure.reason)}
           </EuiCodeBlock>
 
           {index < shardFailures.length - 1 ? <EuiSpacer size="l" /> : undefined}

src/core_plugins/kibana/public/discover/directives/no_results.test.js

@@ -33,11 +33,11 @@ describe('DiscoverNoResults', () => {
         const shardFailures = [{
           index: 'A',
           shard: '1',
-          reason: 'Awful error',
+          reason: { reason: 'Awful error' },
         }, {
           index: 'B',
           shard: '2',
-          reason: 'Bad error',
+          reason: { reason: 'Bad error' },
         }];
 
         const component = render(