Deletion of S3 objects fails for object paths starting with a slash

## Summary

When trying to delete all objects in an S3 bucket, the deletion fails for objects with a leading slash in their path.
The `delete_object` method returns `True` for these objects, even though they are not deleted.

## Detailed Information

To delete an S3 bucket we use `Container.list_objects()` and `delete_object` to first delete all objects in the bucket. This doesn't work for objects, where the object path starts with a slash. The `delete_object` function returns `True` for these objects even though they are not deleted because the DELETE request is sent to the wrong URL.
For example to delete the object `s3://container-name//path/to/object` the DELETE request is sent to
https://s3-eu-west-1.amazonaws.com/container-name/path/to/object
but it should be sent to this path instead:
https://s3-eu-west-1.amazonaws.com//container-name/path/to/object
The problem is that double slashes are replaced in the request URL in the method `Connection.morph_action_hook`. This is a similar issue to #1529.

To reproduce the issue, you can use the following code (replace credentials and bucket name):
```python
from libcloud.storage.types import Provider
from libcloud.storage.providers import get_driver

driver = get_driver(Provider.S3)
client = driver("key", "secret", region="eu-west-1")

container = client.get_container("container-name")
objects = container.list_objects()
for obj in objects:
client.delete_object(obj)
client.delete_container(container)
```
This will result in an `ContainerIsNotEmptyError` if the bucket "container-name" contains objects where the object path starts with a slash.

Libcloud version: 3.4.1
Python version: 3.7.12

从 Connection.morph_action_hook 开始，使用以斜杠开头的对象路径，通过 S3 示例重现该问题。跟踪 DELETE 请求 URL 的规范化过程；当开头的斜杠得到保留、对象确实被删除，并且随后可以删除 bucket 时，即表示完成。

由索引模型根据 Issue 内容生成。