Fix Azure blobstore error instantiating AzureClient

commit 72ce566 "Avoid infinite number of calls to listBlobs when
doing prefix removals (e..g, gridset or layer removals)"
changed the gwc `AzureClient` check for container existence from an
attemp to create it to an attempt to get its properties before creating
it.

When the container doesn't exist, the blocking call throws
`com.microsoft.azure.storage.blob.StorageException`, which contains the
status code.

Wrap that call in a try-catch block and get the status code from the
exception.

Author: groldan

geowebcache/azureblob/src/main/java/org/geowebcache/azure/AzureClient.java

@@ -93,8 +93,13 @@ public AzureClient(AzureBlobStoreData configuration) throws StorageException {
             this.container = serviceURL.createContainerURL(containerName);
             // no way to see if the containerURL already exists, try to create and see if
             // we get a 409 CONFLICT
+            int status;
+            try {
+                status = this.container.getProperties().blockingGet().statusCode();
+            } catch (com.microsoft.azure.storage.blob.StorageException se) {
+                status = se.statusCode();
+            }
             try {
-                int status = this.container.getProperties().blockingGet().statusCode();
                 if (status == HttpStatus.NOT_FOUND.value()) {
                     status = this.container.create(null, null, null).blockingGet().statusCode();
                     if (!HttpStatus.valueOf(status).is2xxSuccessful()