explicitly install ss for ubuntu18 acceptance tests
explicitly install ss for ubuntu18 acceptance tests

this is a workaround until
https://github.com/puppetlabs/beaker-hostgenerator/pull/124/files is
released

puppetlabs/puppetlabs-rabbitmq,voxpupuli/puppet-rabbitmq,Slm0n87/puppet-rabbitmq,puppetlabs/puppetlabs-rabbitmq,Slm0n87/puppet-rabbitmq,voxpupuli/puppet-rabbitmq,Slm0n87/puppet-rabbitmq