[#2032] Update build system to buildbot changes.


Problem description
===================

Buildbot configuration was changed to reduce the customization on buildbot part and user more script from the repo.



Changes description
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Add a new test_ci paver task which will be used by buildbot for running tests.

Update merge_init and merge_commit to get arguments  from environment.


How to try and test the changes
===============================

reviewers @adiroiban

Lets see if this lands.

Thanks!