src/main/java/hudson/plugins/sshslaves/verifiers/KnownHostsFileKeyVerificationStrategy.java only uses the "per-user" file "~/.ssh/known_hosts", but not the global "/etc/ssh/ssh_known_hosts" files. (we roll out that global file to all our hosts to improve security and to remove the "per-user" burdon to verify each host).

As "ssh" does not add the host key to the "per-user" file if it is already in the "global" file, this breaks starting a Jenkins slave per ssh until the keys from the global file are manually copied to the "per-user" file.

The ssh-slaves-plugin should also honor the global file (if it exists).