Previously no hostkeys were checked if they were not present
in the generated configuration file. When the drop-in directory is
used, usually, there are no hostkeys in that file and no sanity
check for hostkeys was executed.
This amends the "auto" value for the hostkeys check to allow checking
for default hostkeys that are read by OpenSSH by default.
Signed-off-by: Jakub Jelen <jjelen@redhat.com>