`ssh.recv_known_host` is known to return `None`, should be flagged as such.
Since `ssh.recv_known_host` is now known to return `None` let's assert it's not `None`.
Enforce `integration.TMP` usage.
Create temporary directories first.
Adapt the test case to saltstack/salt@70b26f30b. Refs #4822
Merge pull request #7082 from s0undt3ch/0.16

[0.16] Fix `ssh.recv_known_host` test case