spec/sqlite hardcoded path to database

(This issue was originally filed by @wiibaa at https://github.com/elastic/logstash-contrib/issues/93)

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Initially reported in https://logstash.jira.com/browse/LOGSTASH-2235

The following line hardcode the absolute path to test-database
https://github.com/elasticsearch/logstash-contrib/blob/master/spec/sqlite-test.rb#L59
