(SERVER-2848) Track puppet-agent#next for updates
(SERVER-2848) Track puppet-agent#next for updates

This commit changes the branch that we track for beaker agent SHAs and
puppet submodule updates to puppet-agent#next, which contains work
landing for Platform 7.

puppetlabs/puppet-server,puppetlabs/puppet-server,puppetlabs/puppetserver,puppetlabs/puppet-server,puppetlabs/puppetserver,puppetlabs/puppetserver,puppetlabs/puppetserver