Checks the known_hosts file (~/.ssh/known_hosts) for the user Jenkins is executing under, to see if an entry exists that matches the current connection.

This method does not make any updates to the Known Hosts file, instead using the file as a read-only source and expecting someone with suitable access to the appropriate user account on the Jenkins master to update the file as required, potentially using the ssh hostname command to initiate a connection and update the file appropriately.