updated to the latest.
Added a mechanism to launch a fixture inside Docker.

This simplifies testing plugins that need to interact with external
systems.
Merge branch 'master' of github.com:jenkinsci/selenium-tests
refactored docker code for better reuse.
refactored a bit
added another command
doc improvement
added a test for scp plugin

... based on https://wiki.jenkins-ci.org/display/JENKINS/LTS+1.532.x+RC+Testing
Integrating docker work into the trunk