Changing logging interface used in _find_master recipe
Adding a defensive case for when no masters are found that prevents accessing a nil attribute hash
Lint for FC and Rubocop
Fix for serverspec v2.0

Syntax changes for new serverspec.
Simplify the slave recipe

- Don't bomb out if master isn't found, fixes https://github.com/rackspace-cookbooks/jenkinsstack/pull/29
- Clean up conditionals to make a much cleaner recipe