Improve rspec formulation in instance_spec
Improve rspec formulation in instance_spec

This change improves readability of the output by putting in proper
messages.

zleswomp/puppetlabs-aws,daveseff/puppetlabs-aws,puppetlabs/puppetlabs-aws,rfletcher/puppet-aws,daveseff/puppetlabs-aws,gregohardy/puppetlabs-aws,marksyme/puppetlabs-aws,benpillet/puppetlabs-aws,marksyme/puppetlabs-aws,zvymazal/puppetlabs-aws,gregohardy/puppetlabs-aws,hundredacres/puppetlabs-aws,hundredacres/puppetlabs-aws,benpillet/puppetlabs-aws,DavidS/puppetlabs-aws,rfletcher/puppet-aws,zvymazal/puppetlabs-aws,zleswomp/puppetlabs-aws,DavidS/puppetlabs-aws,puppetlabs/puppetlabs-aws