Fixes the use of Puppet.warn.
Fixes the use of Puppet.warn.

  This patch converts the final use of Puppet.warn to Puppet.warning.
  Doesn't change any behavior but allows bootstrap action to complete in
  the event that a certname can't be obtained from configprint.  Without
  this the failure to obtain the certname will cause a backtrace.
  This had to be done because the warn method was changed to being a
  private method.

puppetlabs/puppetlabs-cloud_provisioner,amos6224/puppetlabs-cloud-provisioner,16nsk/puppetlabs-cloud_provisioner,puppetlabs/puppetlabs-cloud_provisioner