Ability to specify version directory for training output

[pbarker]

Currently when running swift from the command line it picks a version and outputs the model under that version directory.

This is challenging for automation because you can't parse the created directory from the output, also I may have a different versioning scheme from you.

A user should be able to specify the name of that directory.

[Jintao-Huang]

please use --add_version false

https://swift.readthedocs.io/en/latest/Instruction/Command-line-parameters.html