Support 'xenhvm' for AWS instances

[treydock]

This is on fresh EC2 instance using xenhvm:

$ sudo facter -p virtual
xenhvm

$ sudo facter -p cloud.provider
$

$ sudo facter -p ec2_metadata.system
xen-on-nitro

[puppetlabs-jenkins]

Can one of the admins verify this patch?

[joshcooper]

$ sudo facter -p cloud.provider
$

I would have expected this to return aws

Can you update your commit message to describe how facter behaved before? And how xen-on-nitro is different than xen?

Does /opt/puppetlabs/puppet/bin/virt-what return the expected output?

[treydock]

Updated commit message, will paste here for completeness:

$ sudo facter -p cloud

$ sudo facter -p virtual
xenhvm

$ sudo /opt/puppetlabs/puppet/bin/virt-what
xen
xen-hvm
aws

We have pushed this custom fact to our systems that mimics the logic Facter uses with this PR's addition:

Facter.add('cloud') do
  setcode do
    value = nil
    provider = Facter::Util::Facts::Posix::VirtualDetector.platform
    if ['xenhvm', 'xen', 'kvm'].include?(provider)
      metadata = Facter::Resolvers::Ec2.resolve(:metadata)
      value = 'aws' unless metadata.nil? || metadata.empty?
    elsif ['gce'].include?(provider)
      metadata = Facter::Resolvers::Gce.resolve(:metadata)
      value = 'gce' unless metadata.nil? || metadata.empty?
    end
    if value.nil?
      value
    else
      { 'provider' => value }
    end
  end
end

Using that custom fact that accounts for xenhvm we get this:

$ sudo facter -p cloud
{
  provider => "aws"
}
$ sudo puppet facts show cloud
{
  "cloud": {
    "provider": "aws"
  }
}

[treydock]

@joshcooper Let me know if these changes and the updated commit messages are looking like they could be merged.