The MachineDeployment CRD is going to be removed but currently the cluster-autoscaler component assumes that the resource is present even though it won't scale MachineDeployment-based resources.
The autoscaler needs to be updated to remove any dependency on the MachineDeployment resource being present on the cluster.
Additional PR: https://github.com/openshift/cluster-api/pull/29
$ oc get clusterversion
NAME VERSION AVAILABLE PROGRESSING SINCE STATUS
version 4.1.0-0.nightly-2019-04-22-005054 True False 25h Cluster version is 4.1.0-0.nightly-2019-04-22-005054
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.