Use strainer to isolate and test individual cookbooks

Included:
- Add strainer gem
- Update test-related gems
- Add Strainer file
- Remove run_tests.bash
- Update .gitignore
- Update README file
- Update specs to use require_relative

Partial fix for bug 1188345

Change-Id: I6cb9e535212346cccb45f8c41c647b8daa8a4c7d
Merge "Use strainer to isolate and test individual cookbooks"