We were unconditionally inserting into the yaml cache anything we had
retrieved from the yaml cache.  This had the side-effect of being expensive
on re-runs of commands where yaml hadn't changed.

Signed-off-by: Daniel Silverstone <daniel.silverstone@codethink.co.uk>

_yaml.py: Do not insert into cache if retrieved from cache

See merge request !902

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.