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.
you can omit the `return true` statement here since the `local_branches.include?` statement is a boolean function and will return true/false appropriately.