[krbdev.mit.edu #6522] bugs in generating kadmin service principal name from hostname

[Ken Raeburn via RT]

I think kadm5_get_admin_service_name should be using  
krb5_sname_to_principal.  As the code is now, it doesn't follow the  
same logic for generating the host-based principal names for kadmin as  
we use for other host-based services.  (You can argue that that logic  
in sn2princ is wrong, and we shouldn't be doing the DNS lookups, blah  
blah blah, but I think being inconsistent and wrong in two places is  
worse than being consistently wrong and doing it in one place.)

If there's a reason for it not to use krb5_sname_to_principal, it  
should probably at least force the hostname to lower-case when  
constructing the principal name.  The only reason I can think of is  
consistency with Sun's behavior, but I would think we'd want that more  
globally, or more generally configurable, not just confined to kadmin.