[CI] Added the "simplecov-rcov" gem for Jenkins and separated output for ENV['COVERAGE'] and ENV['CI']

* Jenkins plugin: https://wiki.jenkins-ci.org/display/JENKINS/Ruby+metrics+plugin
* Added the "simplecov-rcov" gem for Jenkins coverage report; https://github.com/fguillen/simplecov-rcov
* Separated formatting the test coverage reports for COVERAGE and CI environment variables

In the end, the support isn't easily possible for this project, since it has four indepependent
sub-projects, and the Jenkins plugin expects a *single* directory with the coverage
report HTML files (as opposed to eg. the jUnit reporter plugin).

The support would have to be implemented by a custom formatter ot custom script,
which would gather the HTML files and transform them into the format expected
by the Jenkins plugin.
[EXT] [CI] Removed the "ANSI" extension from coverage reports

This extension is experimental and non-essential.
Improved formatting for the main Rake testing tasks