remove gem dependency on Vagrant

add locks to gemspec to preserve compatibility with Vagrant 1-0-stable
explicitly require 'berkshelf/vagrant' in spec_helper for testing

add Vagrant to development gemset for testing/development
Merge pull request #288 from RiotGames/remove-vagrant-dep

Berkshelf gem should not depend on Vagrant gem
version bump 1.1.5
Merge branch '1-1-stable'

Conflicts:
	Gemfile
	berkshelf.gemspec
	spec/spec_helper.rb