Reopening a closed workspace is not intuative

Background

It seems to me that a commonly encountered user workflow may involve the following:

• Open workspace to make a change to the source code of an element.
• Close the workspace to go back the using the original sources. This may be to compare behaviour to to work on something else that has become higher priority.
• Reopen the original workspace to continue the original piece of work.

Currently, reopening an existing workspace requires passing the --no-checkout flag to bst workspace open. Trying to reopen an existing workspace without this flag gets the error Checkout directory is not empty: $workspace_directory.

I recommend one of two options:

• Rename the --no-checkout option to something akin to --reopen
• Use --reopen (formerly, --no-checkout) as a default when the target workspace already exists

Acceptance Criteria

It should be obvious to a new user how to reopen a closed workspace.