Change create broken cookbook tests to expect 400 instead of 500.

Works with corresponding change in opscode-chef.
Update depsolver tests to not check error message.

Error message is returned in a different order than expected.
The order shouldn't matter. The message doesn't matter much
either.
Update tests to check double-encoded error response.

Chef client will parse the double-encoded response, so the test
should as well.
Merge pull request #43 from opscode/jpl/ohc_fixes

Change create broken cookbook tests to expect 400 instead of 500.