list_or_* functions (e.g. list_or_string) will now always return a list,
however will accept lists or indivitual values. Also added a list_or()
generator function, similar to what already exists for list_of().
As instrumentation can be enabled/disabled for a specfic workload
execution, it is sometimes not enough to verify that an instrument has
been installed for the run; one might need to check whether it is
currently enabled.
When the merging logic was updated to preserve duplicates within the
same list, it inadvertently broke the logic that removed items marked
for removal with a '~'. This commit rectifies that.
Note to self: merging functions are doing *way* to much; they should be
refactored into several individual function and config should be
resolved in distinct stages.
If list parameter values contained duplicates, those got removed when
merging parameter values from different sources. This commit fixes that
behavor, so that duplcates that appear within the *same* list are
preserved.
