Add acceptance tests

This PR finally adds some rspec based acceptance tests to bills kitchen which run a common usage scenario (see below)

Run into some troubles and downgraded to Ruby 1.9.3 again to fix the issues mentioned in #48 in order to make all tests pass:

The acceptance tests do NOT run as part of `rake build` and have to be run explicitly via `rake acceptance`:
```
D:\Repos\_github\bills-kitchen>rake acceptance
rspec spec/acceptance -fd -c

usage scenarios
  managing base boxes
    imports a local basebox (if exists)
  developing application cookbooks
    clones an application cookbook via `git clone`
    installs gem dependencies via `bundle exec`
    runs the unit tests via `rake test`
    runs the integration tests via `rake integration`
  managing infrastructure
    clones an infrastructure repo via `git clone`
    installs vagrant plugin dependencies via `vagrant plugin bundle`
    brings up a VM via `vagrant up`
    can talk to that VM via `vagrant ssh`
    can provision a VM via `vagrant provision`
    can destroy a VM via `vagrant destroy`

Finished in 13 minutes 43 seconds
11 examples, 0 failures
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