Let NixOps provide known_hosts independently of user known_hosts

Companion of NixOS/nixops#1464

Author: roberth

nixops_aws/backends/ec2.py

@@ -488,6 +488,9 @@ def _ip_for_ssh_key(self):
         else:
             return self.public_ipv4
 
+    def get_ssh_host_keys(self):
+        return self.private_ipv4 + " " + self.public_host_key + "\n" + self.public_ipv4 + " " + self.public_host_key + "\n"
+
     def _booted_from_ebs(self):
         return self.root_device_type == "ebs"