This fixes bugs added as a part of 8665b0638a1d3a70f985126b0f007a26c81273cb

1. if accept_hostkey is false, no matter if the host key is known or not, it will fail.

2. We don't check for the host key in /etc/ssh/ssh_known_hosts

This fixes both of those issues.
Merge pull request #5587 from kormoc/fix_git_check_hostkey_etc

Fixes for git module