Beaver 31 / logstash 1.2 support

[pburkholder]

Hi Lusis,

beaver 31 adds support for logstash 1.2 json schema, but it requires that the beaver.conf have 'logstash_version: 0' or 'logstash_version: 1'

The current beaver recipe doesn't allow any arbitrary configuration options to be passed, or to use a -D conf.d directive. Support for either would help.