Shared helpers to dry out common CI scripts used by plugins.

LogStash plugins by convention store configuration under ci/ folder, .ci is meant to be an optional replacement for most ci/* files.

There's also assumptions about using rspec to write tests currently.

Set up your plugin's .travis.yml:

import:
- logstash-plugins/.ci:travis/defaults.yml@v0.1.0
- logstash-plugins/.ci:travis/matrix.yml@v0.1.0
- logstash-plugins/.ci:travis/exec.yml@v0.1.0

If the plugin follows conventions and (unit) tests all run using rspec, simply place your own shell scripts in the .ci folder