Adds Config Drive Support

Previously, nova did not support forcing config_drive
and users would need to specify the config-drive=true
nova CLI option.  However, Horizon G release is unable
spawn instances using the config-drive=true CLI option.
This change provides the ability for users to fully leverage
config_drive for Nova deployments.

More information on Config Drive can be found here:
  http://http://docs.openstack.org/trunk/openstack-compute/admin/content/config-drive.html

The change implements a new force_config_drive parameter.
The parameter is set to false to maintain backwards compatability.

Change-Id: Ic2fc7c74134a041cba35b6fcd19b0716f7dc7a0e
Merge "Adds Config Drive Support"