Support for input from sources other than files

[maxwellhaydn]

It would be great if this project supported input from sources other than files. For example, we use the JDBC and JDBC static plugins to load data from relational databases into Elasticsearch. We want to write tests that check all aspects of our pipeline config, including:

• Did the configured SQL query/queries select the expected data from the raw data set?
• Did it connect to the right database with the right credentials and connection options?
• Did it filter and transform the raw data correctly before loading it into Elasticsearch?

[agolomoodysaada]

That sounds awesome. This can probably be handled with stdin. We already pass the input logs via stdin here https://github.com/agolo/logstash-test-runner/blob/master/test.sh#L73

PRs are welcome to allow configurable input streams