samba: Fixed tests for undefined variables
samba: Fixed tests for undefined variables

According to
http://docs.puppetlabs.com/guides/templating.html#testing-for-undefined-variables,
undefined variables should be tested with <% if @var %>, otherwise the
text "undef" will be assigned to the variable.

thias/puppet-modules,thias/puppet-modules,thias/puppet-modules,thias/puppet-modules,thias/puppet-modules