Add test for many to many relationship in hosts definition

In order to ensure that the many to many relationship defined between
hosts and IPs continues to work, this commit adds a spec test on the
content generated by the template.
Add focus flag config to spec tests

To make it easier to focus on a single spec test, this commit adds the
RSpec configuration options to allow the use of the focus tag to only
run certain specs.
Ignore .bundle

Bundler uses the .bundle folder for custom options used with bundler,
and these should not be stored in the repo, so this commit adds the
folder name to the gitignore.