Self-Documenting Policies

Provide an alternate policy specification file format based on ConfigParser, then use this format to allow for grouped policies (section "compute_extensions" variable "admin_actions:pause" would correspond to "compute_extensions:admin_actions:pause"). Additionally, allow pre-declaration of policy rules with a default policy and help text, which could then be dumped into an example policy configuration file a la nova/tools/conf/generate_sample.sh.