Update rpsec matchers to use non-deprecated methods

When we upgraded RSpec to RSpec 3.0, we started getting deprecation warnings in our specs because of bbq.

```
Deprecation Warnings:

`failure_message_for_should_not` is deprecated. Use `failure_message_when_negated` instead. Called from /Users/pivotal/.rbenv/versions/2.0.0-p481/lib/ruby/gems/2.0.0/gems/bbq-0.2.1/lib/bbq/rspec.rb:53:in `block in <module:RSpecMatchers>'.

`failure_message_for_should` is deprecated. Use `failure_message` instead. Called from /Users/pivotal/.rbenv/versions/2.0.0-p481/lib/ruby/gems/2.0.0/gems/bbq-0.2.1/lib/bbq/rspec.rb:44:in `block in <module:RSpecMatchers>'.

`match_for_should_not` is deprecated. Use `match_when_negated` instead. Called from /Users/pivotal/.rbenv/versions/2.0.0-p481/lib/ruby/gems/2.0.0/gems/bbq-0.2.1/lib/bbq/rspec.rb:34:in `block in <module:RSpecMatchers>'.

`match_for_should` is deprecated. Use `match` instead. Called from /Users/pivotal/.rbenv/versions/2.0.0-p481/lib/ruby/gems/2.0.0/gems/bbq-0.2.1/lib/bbq/rspec.rb:24:in `block in <module:RSpecMatchers>'.
```

We updated the RSpecMatcher module in bbq to use the updated syntax.