(PUP-3127) LDAP - introduce LDAP-Certificat Directory

Add ldapcrtdir settings to enable ssl based ldap connections on Solaris based Puppet-Master.
Without this implementation it is not possible to create ssl encrypted ldap connections on a Solaris system.
If the 'ldapcrtdir' parameter is not set or set to false (=> default), the connection is etablished as before.
Please change the default to nil, to match how we handle initializing other strings.