Making brew installs commands work in idempotently
Extend and improve osx idempotency

Includes:

* Fix the "brew_install_or_upgrade" function, use it for all components
* Remove executable perms
* Skip installing an already installed ruby

Technically re-running laptop is not idempotent in that it will upgrade
brew-installed items and potentially install a new ruby. I feel this
is expected and wanted.
Remove ruby 2.1.1 conditional behavior for rbenv installation
Be more careful about nvm init in zshrc