Change olcPPolicyHashCleartext for not storing clear text passwords

This attribute/directive tells the server to save cleartext passwords, supplied using normal Add or Modify requests, in the DIT using the server's default hash algorithm. Without this directive the passwords would be stored in cleartext meaning that simple searches would return the cleartext password. To guard against this possibility all password attributes should deny read access for all users (generally a good policy even if hashed passwords are used). This attribute/directive is not necessary if all LDAP clients are known to use Password Modify extended operation.