[COOK-760] - selinux state based on attribute

* Add policy state attribute, enforcing default (matches the RHEL
  default policy)
* Add selinux_state LWRP
* Convert recipes to use LWRP
* Update README, metadata
Merged COOK-760 from the latest Opscode cookbook. Removed my own similar modifications
Fixed up the work begun by J. Timmerman. Added attribute for selinuxtype.