Dynamic scoping for variables in ERB templates was removed in puppet
4[1] which means that the variables defined in the
manifest cannot be found when it is referenced in
the httpd::vhost defined type and will be evaluated as nil when
puppet runs. Use the scope object instead to be explicit about the
variable's source. The scope object and scope.lookupvar return :undef
instead of nil if the variable is undefined, and we expect it to
sometimes be undefined, so handle that too.
[1] https://puppet.com/docs/puppet/4.10/lang_updating_manifests.html#dynamic-scoping-in-erb
Change-Id: Ie9d943424aafa5d1d09586dc2cb61441c6d2628b
cec0248653