server list can sort by and show additional fields

"knife joyent server list" now accepts --sort (name|price|compute_node)
as well as --show (tags,compute_node)

Sorting by compute_node adds extra line break to group zones sharing
compute node together. Sorting is independent of showing extra fields.
Switching to use joyent-cloud-pricing gem, WIP
Finalizing using joyent-cloud-pricing gem
Removing extraneous include
Adding "knife joyent server pricing" command

- This command tallies up all costs across all nodes,
  and supports applying reserve discounts from an external
  YAML file to calculate totals, monthlies, and also 
  any "overages": zones that are outside of the reserve.
Upgrading dependency on joyent-cloud-pricing