Add --cookbook-path to the promote subcommand

[bcandrea]

Unlike other Spork subcommands, --cookbook-path is not supported by spork promote.

This option is apparently needed when running all Spork subcommands in a repo-per-cookbook setup (this might fix #85). For example, when an example cookbook sits in the folder

~/dev/
  example/
    cookbooks/
      example/
        ···
        metadata.rb
        Berksfile
        Berskfile.lock
        ···

regardless of the value used for skip_berkshelf the operation fails. With skip_berkshelf = false:

user@box:~/dev$ knife spork promote production example
ERROR: Berkshelf::BerksfileReadError: Berkshelf::BerksfileReadError

user@box:~/dev$ knife spork promote production example -b example/cookbooks/example/Berksfile
ERROR: Berkshelf::BerkshelfError: LockFileNotFound

user@box:~/dev$ knife spork promote production example -b example/cookbooks/example/Berksfile.lock
ERROR: SyntaxError: /home/user/dev/example/cookbooks/example/Berksfile.lock:3: syntax error, unexpected ':', expecting end-of-input
    path: .

With skip_berkshelf = true:

user@box:~/dev/example$ knife spork promote production example
WARNING: Unloading Berkshelf as skip_berkshelf option found in config
ERROR: Chef::Exceptions::CookbookNotFound: Could not find cookbook 'example' in any of the sources!

Although this seems to point to problems with Berkshelf 3, specifying the cookbook path actually works (even with skip_berkshelf = false):

user@box:~/dev$ knife spork promote production example -o example/cookbooks
Adding version constraint example = 0.1.1
Saving changes to production.json
Uploading production.json to Chef Server
Promotion complete at 2015-01-12 15:12:58 +0000!

[jonlives]

@bcandrea Awesome, thanks for this - will get this out with the next release.