Fix logger when you can not create an azure storage client

We were swallowing the original exception when creating a client with bad credentials.
So even in `TRACE` log level, nothing useful were coming out of it.
With this commit, it now prints:

```
[2016-09-27 15:54:13,118][ERROR][cloud.azure.storage      ] [node_s0] can not create azure storage client: Storage Key is not a valid base64 encoded string.
```

Closes #20633.

Backport of #20669 for master branch (6.0)

plugins/repository-azure/src/main/java/org/elasticsearch/cloud/azure/storage/AzureStorageServiceImpl.java

@@ -175,7 +175,7 @@ public class AzureStorageServiceImpl extends AbstractComponent implements AzureS
             blobContainer.createIfNotExists();
         } catch (IllegalArgumentException e) {
             logger.trace((Supplier<?>) () -> new ParameterizedMessage("fails creating container [{}]", container), e);
-            throw new RepositoryException(container, e.getMessage());
+            throw new RepositoryException(container, e.getMessage(), e);
         }
     }