(MAINT) Pin tests to puppet-agent 1.8.1
(MAINT) Pin tests to puppet-agent 1.8.1

CI has begun failing because the sha we were previously pinned to no longer
has artifacts on the builds server

rlinehan/puppet-server,puppetlabs/puppetserver,rlinehan/puppetserver,rlinehan/puppet-server,rlinehan/puppetserver,puppetlabs/puppetserver,camlow325/puppetserver,puppetlabs/puppet-server,puppetlabs/puppet-server,camlow325/puppetserver,er0ck/puppetserver,shrug/puppet-server,camlow325/puppet-server,camlow325/puppet-server,shrug/puppet-server,er0ck/puppetserver,shrug/puppet-server,puppetlabs/puppet-server,puppetlabs/puppetserver,camlow325/puppetserver,camlow325/puppet-server,rlinehan/puppetserver,rlinehan/puppet-server,er0ck/puppetserver,shrug/puppet-server,camlow325/puppetserver,er0ck/puppetserver,rlinehan/puppetserver,puppetlabs/puppetserver