Changed the option names to --description and --affinity-group

Changed the option names to --description and --affinity-group on the storage command. This is the same options as used on other commands in the CLI (vm disk, vm image).

This is a replacement for PR https://github.com/WindowsAzure/azure-sdk-tools-xplat/pull/173 and is now based on the dev branch.

One issue is that setting a description on the create storage command does not work! But that did not work before this change either. I checked the code in the CLI and SDK projects and I cannot find any obvious bugs. Is the support missing on the server side? Setting a description on the storage update command is working as expected.