To disable ssh warning message we need to add LogLevel to quiet in $HOME/.ssh/config file.
We can also diable warning messages with ssh command as shown below:
$ ssh -o LogLevel=quiet 192.168.1.10
With following example we can also disable Host Key Checking, set known hosts file to null and disable logging:
$ ssh -o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no -o LogLevel=quiet 192.168.1.20