Initial attempt at perl test framework

Support new-style perl tests (e.g. `test/logstash_v1.2.t`).
Main improvements are
* proper factored out code with unittests
* improved testing, in particular support for `ordered` testing

Depends on https://github.com/quattor/maven-tools/pull/27
The test framework itself is supposed to be merged into `maven-tools` at some point as it can help with unittesting TT files outside of metaconfig usage.