racktables - outdated variable syntax

"Warning: Variable access via 'racktables_host'
is deprecated. Use '@racktables_host' instead."

etc..

https://projects.puppetlabs.com/issues/19058

Change-Id: I374a3a657486798f16c23e4b2b3d93010f9dc17a
Merge "racktables - outdated variable syntax" into production