Added show-deps option to CLI.

Simply shows the dependency for the given recipe. It would help to show package list to be able to give package manager such like yum or apt-get.

```
$ bundle exec fpm-cook recipes/omnibustest/recipe.rb show-deps
libffi6 libncurses5 libreadline6 libssl1.0.0 libtinfo5 libyaml-0-2 zlib1g libgdbm3 autoconf libreadline6-dev bison zlib1g-dev libssl-dev libyaml-dev libffi-dev libgdbm-dev libncurses5-dev
```