Yum provider raises exception if check-update returns unexpected exit code

Installing PE 2015.2.3 on an AWS instance without internet access fails to install the console successfully.

The yum package provider calls `yum check-update`, and the command returns a non-zero exit code. The package provider tries to emit a warning, but calls a private method in doing so. This causes an exception to be raised and the resource to fail.

[2015-11-19 16:52:16.287 UTC] INFO Error: Could not get latest version: private method `warn' called for Puppet::Type::Package::ProviderYum:Class

[2015-11-19 16:52:16.287 UTC] INFO Error: /Stage[main]/Pe_nginx/Package[pe-nginx]/ensure: change from 1.8.0-9.pe.el7 to latest failed: Could not get latest version: private method `warn' called for Puppet::Type::Package::ProviderYum:Class

Steps to workaround the issue:
1. Run installer
2. Modifed /opt/puppetlabs/puppet/lib/ruby/vendor_ruby/puppet/provider/package/yum.rb:83, commenting out the `warn` directive
3. Proceed with installation in GUI

This is probably a trivial fix to the yum provider: update it to emit a warn correctly without raising an exception.