add buildbot_run_id to sql_reporter plugin

Uniqueness of the buildbot_run_id is enforced by buildbot (configuration).
go back to using a constant string instead of uuid4 in test
add buildbot_run_id to test results as well.
better tests & cleanup
do not duplicate buildbot_run_id in test_results table
Merge pull request #143 from baris/bmetin_buildbot_run_id

add a unique buildbot run identifier