fix: replace ensure-bucket-exists command with ensure-storage-exists

- It is implemented as storage exists to generalize to  bucket, container or storage for different iaas providers

Author: serdarozerr

lib/cloud_controller/blobstore/storage_cli/storage_cli_client.rb

@@ -162,7 +162,7 @@ def files_for(prefix, _ignored_directory_prefixes=[])
       end
 
       def ensure_bucket_exists
-        run_cli('ensure-bucket-exists')
+        run_cli('ensure-storage-exists')
       end
 
       private