All other REST endpoints for comments have a clear separation between
published comments and draft comments. We follow the same approach for
ported comments and hence introduce a dedicated REST endpoint for
ported draft comments.
The existing tests for ported comments also cover most code paths for
ported draft comments as a large amount of the code is shared. We only
add additional tests for varying aspects or those which are outside of
the shared code.
Change-Id: If8802a4f94540284cc1303b278f7f38d120593eb
bd543094f8