Benjamin Schubert authored Oct 25, 2018 and Benjamin Schubert committed Oct 26, 2018

Currently we would make sure the sandbox had a command before
converting it to a list if it was given as a string. That meant that a string
command would never exist and the check be invalid.

This also adds the same logic in the dummy sandbox for consistency.

Check is command is a str and replace by list before checking existence

Closes #728

See merge request !898