[gcloud] Do not raise an exception when trying to delete a non-existe…

…nt blob (#999)

Closes #998

storages/backends/gcloud.py

@@ -162,7 +162,10 @@ def _save(self, name, content):
 
     def delete(self, name):
         name = self._normalize_name(clean_name(name))
-        self.bucket.delete_blob(name)
+        try:
+            self.bucket.delete_blob(name)
+        except NotFound:
+            pass
 
     def exists(self, name):
         if not name:  # root element aka the bucket