Add oj as a testing dependency

Chef now vendors Yajl, which significantly increases the time it takes to run
the cucumber tests. It also throws occasional errors because multi_json isn't
completely compatible with Yajl. Oj makes the tests fast and awesome.
Add +have_state_attrs+ matcher

- Closes #251
Use a temporary directory for cucumber tests to silence Travis
Test against Chef 11.8.0
Add a link to knife-spec [ci skip]
Convert all dashes to underscores before stepping into an LWRP
Add Joe Goggins quote to README