Fixed pointer to a variable in puppetagent module

The variable $::puppetagent::params::ssl_dir was recently renamed as
$::puppetagent::params::ssldir, but Bacula was still using the old variable
name. This caused failures to copy Puppet certificates to Bacula's directory.

Signed-off-by: Samuli Seppänen <samuli.seppanen@gmail.com>