Add PE simplified agent startup script

This commit adds a new startup script to the available options. It
is based on the simplified agent (package-based) install available
with the latest version of Puppet Enterprise.
By default, it will work in collaboration with a PE Master of the
same operating system family. README update coming in a separate
commit.
Enable trusted autosigning for PE agents

This commit adds all the bits necessary to enable policy-based
autosigning of Puppet Enterprise agents in GCE with a PE master
also in GCE.

With changes in this commit, PE Masters classified using the
gce_compute::autosign class and assigned a compute-ro service scope
combined with PE Agents provisioned using the pe-simplified-agent
will connect to each other with no intervention on behalf of the user.

The startup script retrieves its unique id from GCE metadata and
stuffs it into the csr it makes to the PE master. The PE master
queries the google compute API for this metadata and compares it to
what's in the csr.
Rehabiliate README.md

This commit gives some love to the modules README. It includes a
description of the trusted autosigning added by previous commits
and improves the quick start examples, largely based on the
GoogleCloudPlatform demo instructions. The README could use a lot
more attention but this is sufficient for now.
Better handling of the csr_attributes.yml file

This commit corrects how the pe-simplified-agent.sh script handles
the csr_attributes.yml file. Instead of deleting it, potentially
before the first Puppet run, the script will instead change
ownership to pe-puppet and change mode to 0600.
Merge pull request #28 from ryanycoleman/frictionless

1000% percent improvement with PE agent installs