Drastically refactor and simplify IPMI discovery and config.

* Refactor the discover and configure recipes with an eye towards
  simplicity and longer-term maintainability.
* Add a library of helper functions in an IPMI module.
* Kill off the now-redundant resources and providers.
  RHEL 6 ipmitools is smart enough about timeouts to no longer require
  the weird ad-hoc test/set/sleep/test thing we were doing with them.
* Add a bunch of attributes to expose IPMI information we care about to
  everyone else.