Issue title: Docker driver ignores docker_host  in molecule.yml
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# Issue Type

- Bug report

# Molecule and Ansible details

```
ansible --version && molecule --version
ansible 2.9.12
  config file = /etc/ansible/ansible.cfg
  configured module search path = ['/home/knagamin/.ansible/plugins/modules', '/usr/share/ansible/plugins/modules']
  ansible python module location = /home/knagamin/.local/lib/python3.8/site-packages/ansible
  executable location = /home/knagamin/.local/bin/ansible
  python version = 3.8.5 (default, Jul 31 2020, 00:00:00) [GCC 10.2.1 20200723 (Red Hat 10.2.1-1)]
molecule 3.0.4
```

Molecule installation method (one of):

- pip

Ansible installation method (one of):

- pip

# Desired Behavior

Molecule runs with a correct docker host when the host is specified in molecule.yml like:
```
driver:
  name: docker
platforms:
  - name: instance01
    docker_host: tcp://docker.test.local:2375
```

# Actual Behaviour

Docker driver will always try to connect to localhost if `DOCKER_HOST` is not defined.
Because the driver refers to default host (unix://var/run/docker.sock) instead of that.
Then `docker_host` attribute is ignored.
This issue will produce the sanity check failure and runtime error. 

Workaround for this is using `DOCKER_HOST` environment variable.
 Comments: 
 Comment 0: This issue may include #2614
 Comment 1: It is not only the `docker_host` but also 
```
cacert_path: /foo/bar/ca.pem
cert_path: /foo/bar/cert.pem
key_path: /foo/bar/key.pem
```
Setting `DOCKER_CERT_PATH=/my/path/` helps
 Comment 2: @stiller-leser It’s right. And `DOCKER_TLS_VERIFY` too in that sense. These three environment variables are also referred in provisioner for docker. But I think it’s not good to make the scope broad. If we include many things, it’ll be more complex to fix.
 Comment 3: But they are referenced as configuration for the provisioner in https://molecule.readthedocs.io/en/latest/configuration.html#docker - So they should already be included, no?
 Comment 4: Probably yes and no.

You could see which settings are referred from environment variables for the provisioner [1] and how docker is executed with ansible [2]. The provisioner refers to settings in molecule.yml prior to env or default value. But docker driver might override a only docker host option by adding a env value to `ansible_docker_extra_args`.  Furthermore, only environment variables are used in sanity check. [3]

[1] https://github.com/ansible-community/molecule/blob/master/molecule/provisioner/ansible/playbooks/docker/create.yml
[2] https://github.com/ansible-community/molecule/blob/master/molecule/driver/docker.py#L219
[3] https://github.com/ansible-community/molecule/blob/master/molecule/driver/docker.py#L234
{'source': 'GithubIssues', 'repo_name_with_owner': 'ansible-community/molecule', 'issue_id': 681717557, 'repo_stars': 983.0}