Add API v3 endpoint support

Nova API v3 is now by default in Icehouse. This patch aims to add the
ability to create the endpoint or not.

Change-Id: I66c6c9b439f8320cd56b6899d02bbe01b80f7243
Signed-off-by: Emilien Macchi <emilien.macchi@enovance.com>
Merge "Add API v3 endpoint support"
Merge git://github.com/puppetlabs/puppetlabs-nova