Fix test_ssh_kwargs to not access /etc/salt/pki

[bdrung]

Running the SSH unit tests without root permission fails:

$ python3 -m pytest tests/pytests/unit/client/ssh/test_ssh.py
[...]
Traceback (most recent call last):
  File "salt/client/ssh/__init__.py", line 264, in __init__
    salt.client.ssh.shell.gen_key(priv)
  File "salt/client/ssh/shell.py", line 36, in gen_key
    os.makedirs(os.path.dirname(path))
  File "/usr/lib/python3.9/os.py", line 215, in makedirs
    makedirs(head, exist_ok=exist_ok)
  File "/usr/lib/python3.9/os.py", line 215, in makedirs
    makedirs(head, exist_ok=exist_ok)
  File "/usr/lib/python3.9/os.py", line 225, in makedirs
    mkdir(name, mode)
PermissionError: [Errno 13] Permission denied: '/etc/salt/pki'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "tests/pytests/unit/client/ssh/test_ssh.py", line 134, in test_ssh_kwargs
    ssh_obj = client._prep_ssh(**opts)
  File "salt/client/ssh/client.py", line 125, in _prep_ssh
    return salt.client.ssh.SSH(opts)
  File "salt/client/ssh/__init__.py", line 266, in __init__
    raise salt.exceptions.SaltClientError(
salt.exceptions.SaltClientError: salt-ssh could not be run because it could not generate keys.

Changing the accessed directories to temporary directories would be a solution:

    client.opts["pki_dir"] = tmpdir.join("pki").strpath
    client.opts["cachedir"] = tmpdir.join("cache").strpath

But running the 38 tests takes 130 seconds on an Intel Core i7-8850H CPU @ 2.60GHz. So mock all functions and methods that try to write to the pki or cache directory. Then the tests will succeed in a few seconds.

[bdrung]

Just rebased on master.

[bdrung]

Rebased on master.