[BuildStream] Bst workspace - UX feedback and change suggestions

[Phillip Smyth <phillip smyth codethink co uk>]

Hi everyone,

Today I did a UX test with one of our newer contributers to see how intuitive the bst workspace UI is, and 
got some points that I feel are worth raising.

I gave the engineer the following directions:

"""
Please do not touch the `files` directory in the project dir.
You may look inside the `files` directory, but you may not modify or execute anything in there.

Use bst workspace to modify the existing project from printing "Hello World" to "Goodbye World"
Execute the program to confirm this worked.

Finally please remove the workspace and confirm the dirctory is gone and that there are no more active 
workspaces.
"""

This is a repo of the project i used:
https://gitlab.com/knownexus/hello-project

> From this I got the following feedback and reactions:

1) `bst workspace open` was not clear that it would automatically create the named directory if it did not 
exist.
    This resulted in making the process feel more clunky and is the opposite of `bst init` which does not 
create a named directory, which makes the UX inconsistent.

2)  The closing of a workspace was not intuitive.
    The user expected the directory to be deleted when closing the workspace.
    And for the keeping of the directory to be the flag, not deletion of it.

    A potential fix to this could be:
    Diff the closing workspace, with a temporary new workspace, to see if any changes were made.
    If no changes were made, remove the directory.
    If changes are detected, display a prompt asking if the user wishes to continue deleting all changes 
made, and to re-run the command using `--keep-dir` if they wished to keep the directory.

3) `bst workspace list` displays `[]` when no workspaces are found, instead of showing a message like "No 
workspaces found".
    This would be far clearer than simply printing an empty list.

I believe there are more UX features that could be addressed beyond that of workspaces, and would encourage 
others to do a similar process with other new and existing features,
as I feel it helped a lot to get a fresh perspective and remove my own bias as a factor.

Best regards,

Phillip (Nexus)

-- 
Phillip Smyth, Software Engineer                           Codethink Ltd
Telephone: +44 7762 840 414        3rd Floor, Dale House, 35 Dale Street
https://www.codethink.co.uk/          Manchester, M1 2HF, United Kingdom
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