Restructure rc.d scripts for kerberos5 daemons:

- Rename $kerberos5_server_enable with $kdc_enable and rename
  rc.d/kerberos with rc.d/kdc.

- Rename $kadmin5_server_enable with $kadmind_enable.

- Rename ${kerberos5,kpasswdd}_server with ${kdc,kpasswdd}_program.

- Fix rc.d/{kadmind,kerberos,kpasswdd,kfd} scripts not to change variables
  after load_rc_config().

- Add rc.d/ipropd_master and rc.d/ipropd_slave scripts.  These are
  for iprop-master(8) and iprop-slave(8).  Keytab used for iprop service is
  defined in ipropd_{master,slave}_keytab (/etc/krb5.keytab by default).

- Add dependency on rc.d/kdc to SERVERS.  rc.d/kdc must be invoked as early
  as possible before scripts divided by rc.d/SERVERS.

Note that changes to rc.d/{kdc,kpasswdd,kadmind} are backward-compatible
with the old configuration variables:
${kerberos5,kpasswdd,kadmin5}_server{,_enable,_flags}.