add-resume-option-to-integrate-command

### Changelog
* added in --resume flag to integrate command
* added in —resume feature-branch flag to integrate command to resume
integration after fixing merge conflicts
* added tests for resume feature
* fixed stub_execution for testing run_cmd

* Fix git start command to detect when branch already exists locally.
I think it would be nice to only need one option to pass from the command line. I would prefer to use `--resume` with the feature branch passed in than needing to use `--resume --feature_branch my-feature-branch`.  the extra flag seems superfluous.