r21434: - get rid of "krb5Key"

r21434: - get rid of "krb5Key"
- use "sambaPassword" only as virtual attribute for passing
  the cleartext password (in unix charset) into the ldb layer
- store des-cbc-crc, des-cbc-md5 keys in the Primary:Kerberos
  blob to match w2k and w2k3
- aes key support is disabled by default, as we don't know
  exacly how longhorn stores them. use password_hash:create_aes_key=yes
  to force creation of them.
- store the cleartext password in the Primary:CLEARTEXT blob
  if configured

TODO:
 - find out how longhorn stores aes keys
 - find out how the Primary:WDigest blob needs to be constructed
   (not supported by w2k)

metze