Support Berkshelf3

## WHY

* [Xcode 5.1.1 Release Notes](https://developer.apple.com/library/ios/releasenotes/developertools/rn-xcode/xc5_release_notes/xc5_release_notes.html)

> The Apple LLVM compiler in Xcode 5.1 treats unrecognized command-line options as errors. This issue has been seen when building both Python native extensions and Ruby Gems, where some invalid compiler options are currently specified.
>
Projects using invalid compiler options will need to be changed to remove those options. To help ease that transition, the compiler will temporarily accept an option to downgrade the error to a warning:
>
-Wno-error=unused-command-line-argument-hard-error-in-future

* [2.x to 3.0 Upgrade Guide](https://github.com/berkshelf/berkshelf/wiki/2.x-to-3.0-Upgrade-Guide)

## WHAT

* Support for Berkshelf3
* Use system ruby and gem to install Chef (to avoid native extension issue)
* Add `ARCHFLAGS_OPTION` to `gem install` (to avoid native extension issue)
* Temporary exclude installing cask (for business team)