This was a significant breaking change that was landed despite explicit
disagreement by some community members (myself included). It has already
resulted in an accidental Ironic CI breakage, has broken Bifrost and has
a potential of breaking Metal3. In case of Metal3, MD5 support is a part
of its public API.
While MD5 is a potential security hazard, I don't see the need to hurry
this change without giving the community time to prepare. This change
reverts the new option md5_enabled to True.
Change-Id: I32b291ea162e8eb22429712c15cb5b225a6daafd
c1c5537ba2