This landed with a slightly modified scope: cleaning now works out-of-box, if enabled by setting "clean_nodes = True" in undercloud.conf. We need a separate RFE if we want it by default.
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.
For information on the advisory, and where to find the updated
files, follow the link below.
If the solution does not work for you, open a new bug report.
https://access.redhat.com/errata/RHEA-2017:1245