Return password-only preauth if passwords are allowed
Before this patch, if either password or password+otp were permitted,
only the otp preauth mech would be returned to the client. Now, the
client will receive either enc_ts or enc_chl in addition to otp.
https://fedorahosted.org/freeipa/ticket/433
Reviewed-By: Sumit Bose <sbose@redhat.com>