cluster-api: New release is breaking old clusterctl

What steps did you take and what happened: Ran clusterctl init --infrastructure aws to install CAPI onto my kind cluster. Ran clusterctl config ... | k apply -f- to create a cluster as the init succeeded, but then get errors from the webhook controllers like

Error from server (InternalError): error when creating "STDIN": Internal error occurred: failed calling webhook "default.cluster.cluster.x-k8s.io": Post https://capi-webhook-service.capi-webhook-system.svc:443/mutate-cluster-x-k8s-io-v1alpha3-cluster?timeout=30s: dial tcp 10.102.79.72:443: connect: connection refused
Error from server (InternalError): error when creating "STDIN": Internal error occurred: failed calling webhook "default.machinedeployment.cluster.x-k8s.io": Post https://capi-webhook-service.capi-webhook-system.svc:443/mutate-cluster-x-k8s-io-v1alpha3-machinedeployment?timeout=30s: dial tcp 10.102.79.72:443: connect: connection refused

Saw that the capi-controller-manager deployment was failing in capi-webhook-system, this is the logs of the pod:

invalid argument "MachinePool=${EXP_MACHINE_POOL:=false},ClusterResourceSet=${EXP_CLUSTER_RESOURSE_SET:=false}" for "--feature-gates" flag: invalid value of MachinePool=${EXP_MACHINE_POOL:=false}, err: strconv.ParseBool: parsing "${EXP_MACHINE_POOL:=false}": invalid syntax

What did you expect to happen: Components come up and work as before.

Anything else you would like to add:

clusterctl version: &version.Info{Major:"0", Minor:"3", GitVersion:"v0.3.6", GitCommit:"beff1e1df8e80d3a4fdb996c86409793ee491d47", GitTreeState:"clean", BuildDate:"2020-05-15T16:00:09Z", GoVersion:"go1.13.8", Compiler:"gc", Platform:"linux/amd64"}

Environment:

• Minikube/KIND version: kind v0.8.1 go1.14.2 linux/amd64
• OS (e.g. from /etc/os-release): Linux

/kind bug /area clusterctl