Exit with error status on failed command

When we detect a failed command we log ERROR but we do not return an
error status. This makes it difficult for programs which may run
os-collect-config to detect whether a run was sucessful.

This only applies to runs which are performed with --one-time argument
as this is a straightforward case.

Change-Id: I168862e8c75c15d1ea405a417908d1284feb7b32