Make the raid-discovery role discover raid controllers.

For now, it will only work with RAID controllers that megacli and
sas2ircu support.  WSMAN support has been removed for now until we come
up with a good story for inband vs. out-of-band management.
Merge pull request #10 from VictorLowther/add-raid-discover-role

Make the raid-discovery role discover raid controllers.