Account for list values in def->api translation

In a pipeline definition file, if a value is a list, then
we need to create individual elements (of the same key) for
each element in the list.  Otherwise we get a botocore validation
error as we're trying to send an invalid request.
Add entry to changelog
Merge branch 'pipeline-list-fix' into develop

* pipeline-list-fix:
  Add entry to changelog
  Account for list values in def->api translation