--bootstrap-type on create cluster should work with minikube

[rnandi]

/kind bug

What steps did you take and what happened:
Followed the getting started guide on cluster-api-provder-aws to create a cluster with --bootstrap-type minikube

What did you expect to happen:
I expected it to succeed since clusterctl README indicates that although kind is preferred, minikube is still a valid option

Anything else you would like to add:
Error on running create cluster

create_cluster.go:61] could not create bootstrap cluster: could not create bootstrap control plane: error running command 'minikube start --bootstrapper=kubeadm --p=clusterapi': exit status 64
$ minikube start --bootstrapper=kubeadm --p=clusterapi
Error: unknown flag: --p

Environment:

• Cluster-api-provider-aws version: {GitReleaseTag: "v0.2.0", MajorVersion: "0", MinorVersion:"2", GitReleaseCommit:"e4b898551a60f6", GitTreeState:"clean"}
• Minikube version: v1.0.0
• Kubernetes version: (use kubectl version): N/A
• OS (e.g. from /etc/os-release): N/A