Use an options struct for Resize.
Extended create, rebuild and resize opts.
*JSONEquals() testhelper methods.

These are helpful for testing .ToXyzMap() methods, in particular.
It's "diskConfig", camelCase.
Test request body generation.
Extended ResizeOpts test.
Move Get and Update mocks to fixtures.
diskconfig.Extract* functions.
Move HandleServerListSuccessfully() to fixtures, too.
Unit test for the Extract function.
rackspace.CreateOpts unifies Rackspace opts.
Use keys and diskConfig in RS acceptance tests.
Unit testing grammar :lipstick:
Do the same for Rackspace RebuildOpts.
Use Rackspace rebuild options.
Use ResizeOptsBuilder, not ResizeOpts.
Merge pull request #256 from smashwilson/disk-config

Extension: Disk Config