Make missing known hosts file message a verbose message

Since ansible does not completely implement a OpenSSH option parser it
does not really know which known hosts file needs to be used. Therefore
a faulty message appears if eg a GlobalKnownHosts file is used or a
non-standard UserKnownHosts file as specified by ~/.ssh/config or eg
/etc/ssh/ssh_config. Therefore the message a about the known hosts files
not being found should be only shown if VERBOSITY is at least 1.