Add a command 'clean-workspace-local' to clean workspace directory

+add this command when launch 'cleanup' command
Fix an off-by-one.

(Thanks, @daniellee! https://groups.google.com/forum/#!msg/git-tfs-dev/kiRE5FB5RKI/xh_sxkH-2H8J)
Run Cleanup only when previous succeed
Merge pull request #269 from pmiossec/clean_workspace_dir

Clean workspaces directory with deleting content when Cleaning workspaces