Refactor Berkshelf integration to own class
Refactor Librarian integration to own class
Always gitignore cookbooks/ on init

Unless `--no-git` is specified, that is.
Improve `solo init` logic with Berkshelf and Librarian-Chef

Earlier `knife solo init` defaulted to `--berkshelf`. Then if berkshelf
gem if not installed but Berksfile exists, a warning is issued while
cooking.

New rules to select the default action (first one that matches):

1. `:berkshelf` or `:librarian` specified by CLI option or Knife
   configuration.
2. If Berksfile or Cheffile is found, default to the corresponding option.
3. If berkshelf or librarian gem is found, default to corresponding option.
4. Don't init neither, but inform the user.

Berkshelf takes precedence over Librarian. One or both can be denied
with a --no-option.
Add CookbookManager module

Extract common functionality from Berkshelf and Librarian classes.
Add CookbookManagerSelector class

Also move bootstrap code to CookbookManager classes.
Use ~/.berkshelf/knife-solo/<hash> as default instead of a tempdir
Merge branch 'master' into init-berks-librarian
Small code cleanups
Use config_value helper for :git option
Switch all EC2 ip's to DNS

This lets us avoid potential host key problems by putting this in ~/.ssh/config

```
Host *amazonaws.com
  StrictHostKeyChecking no
```
Merge pull request #250 from matschaffer/dns-access-for-integration

Switch all EC2 IPs to DNS
Pin minitest down to < v5.0.0

The new major release issues warnings on unit tests and break
integration tests.
Fix integratins tests

- Use "site-cookbooks" instead of "cookbooks" as the latter can and will
  be nuked by Librarian and Berkshelf.

- Init kitchens without Berksfile or Cheffile so that they do not
  interfere when cookin.

Both fixes should be enough also alone, but together they should avoid
surprises in the future too.

Also add name attribute to "secret_cookbook".
Merge pull request #240 from tmatilai/init-berks-librarian

Improve `solo init` logic with Berkshelf and Librarian-Chef