Qt Workflow plugin should ping coin with merged shas

When an integration passes, the qt workflow plugin for gerrit merges changes into the target branch. First, a Fast-Forward strategy is tried. If that fails, changes are cherry-picked onto the target branch one-by-one. This latter behavior ultimately results in new commits being generated during the merge process. As a result, COIN data is no longer up-to-date and references shas which may not exist in the final git history following the merge.

To resolve this, the qt workflow plugin for gerrit should perform the merge action and respond to COIN with the resulting shas of each merged change. The plugin should additionally include the sha which sits on top of the commit stack, representing the sole sha from the integration which includes all other tested changes when examining the target branch following the merge.