cask/test: DRY up tests and remove redundant helper

brew info: include options to dependencies in display

Refactor `spec_helper`.

hbc/cli/list: don't require Caskroom to be initialized

fix 'cask info' for external repos with numbers

Also use `which` to find `lsar` in PATH.

Unset HOMEBREW_DEVELOPER in cask tests likely to raise deprecation errors

hbc/locations: arg is file only if absolute or .rb file

fixes 2 issues: error when username has a number, correct url for repos not on github

brew.sh: tweak xcode hint to auto-accept license

Small improvement to the xcode license hint. Reduces friction by allowing user to accept the license in a single step. 
Reference: http://apple.stackexchange.com/questions/175069/how-to-accept-xcode-license

Refactor `brew cask style` not to require `.rubocop.yml`.

Handle the case when an argument passed to `brew cask` is both the name
of a Cask and a non-Cask file in the current working directory.

Fixes https://github.com/caskroom/homebrew-cask/issues/25611.

Look for container extraction programs in PATH.

Set `HOMEBREW_NO_EMOJI` and `HOMEBREW_CASK_OPTS` in `cask-tests`.

Cask update error msgs

audit: don't complain about trailing whitespace.

This is handled by `brew style` now.