Add TryToDeleteWorkspace method for reliability

Refactored the workspace.Delete() action into a TryToDeleteWorkspace method. Includes alternate Retry.Do() values of 5 second delay between tries to help with busy TFS servers. Refined this pull request to minimise code changes as per @spraints and @pmiossec suggestions. Should help improve cloning reliability identified in #570, #461
Forgot to pull latest code and rebase prior to sending PR. Sorry.
Rather than printing "Yes" or "No", how about making it show one of these:

> TFS Workspace '{0}' was removed.
> TFS Workspace '{0}' could not be removed.