10regen-sshkeys: delete all default keys

if for any reason a new cipher is introduces delete all keys
that we haven't regenerated. this might prevent ssh from loading,
but it will avoid leaving default keys in place.

Signed-off-by: Peter Lieven <pl@kamp.de>
10regen-sshkeys: restart sshd only if it is running

Signed-off-by: Peter Lieven <pl@kamp.de>