Create new branch only if it doesn't exist, otherwise it errors

Created by: eesaanatluri

The git_commit agent task status would be true if everything goes well the first time but on a repeated request it would raise an exception that the branch already exists and the task_manager would set the task status false as it saw an exception. So the admin would get a report with git_commit agent status set false even though it ran as expected the first time. To avoid this we add a check to see if the branch doesn't already exist, only then we would create a new branch and commit ldif files to it.