Add storage size to available hosts table

The blockdevice size fact reported by facter will be shown for all block
devices reported on the available hosts table.
Add storage to assigned and free hosts tables

* Pull the table out into a partial
* Add the storage column
* Fix the CPU display
  - Would never display because of:
    * host.cpus if host.respond_to?(:cpu)
Add blockdevices to host_details_helper

Also add the HostDetailsHelper concern to discovered hosts
Remove the need for explicit nil check on blockdevices
Merge pull request #318 from bcrochet/total_disk_avail

Add storage size to available hosts table