Add ability to disable pki_setup

The enable_pki_setup parameter adds the ability to disable pki_setup,
allowing the user to manage the signing certificate himself.

Change-Id: Icb84e01adecdd3287ceb22defb9882f03ae8d96f
Closes-bug: #1278546
Merge "Add ability to disable pki_setup"
Merge git://github.com/puppetlabs/puppetlabs-keystone