Fix KeyError when creating a new secret

[feliperuhland]

How to reproduce the issue:

>>> import docker
>>> cli = docker.from_env()
>>> cli.secrets.create(name="any_name", data="1")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/docker-py/docker/models/secrets.py", line 10, in __repr__
    return "<%s: '%s'>" % (self.__class__.__name__, self.name)
  File "/home/docker-py/docker/models/secrets.py", line 14, in name
    return self.attrs['Spec']['Name']
KeyError: 'Spec'

The exception raises because create secrets API /secrets/create only
return the id attribute:
https://docs.docker.com/engine/api/v1.41/#operation/SecretCreate
The secret model is created using just the id attribute and fails
when looking for Spec.Name attribute.

def __repr__(self):
    return "<%s: '%s'>" % (self.__class__.__name__, self.name)

@property
def name(self):
    return self.attrs['Spec']['Name']

I came up with a ugly solution but will prevent the problem to happen
again:

def create(self, **kwargs):
    obj = self.client.api.create_secret(**kwargs)
+   obj.setdefault("Spec", {})["Name"] = kwargs.get("name")
    return self.prepare_model(obj)

After the API call, I added the name attribute to the right place to be
used on the property name.

>>> import docker
>>> cli = docker.from_env()
>>> cli.secrets.create(name="any_name", data="1")
<Secret: 'any_name'>

It isn't the most elegant solution, but it will do the trick.
I had a previous PR #2517 when I propose using the id attribute
instead of name on the __repr__ method, but I think this one will be better.

That fixes #2025

EDIT: It will save a new request to get the name.

[ulyssessouza]

LGTM

[aiordache]

Thank you