Cluster-api-provider-aws: Need to set ProviderID on common Machine objects

[detiber]

/kind bug

What steps did you take and what happened:
Deploy a machine using cluster-api-provider-aws, the machine Spec.ProviderID field will be empty

What did you expect to happen:
The Spec.ProviderID field should be set with a string in the same format as is populated by Spec.ProviderID on a Node object.

/priority important-longterm
/milestone v1alpha1

[vincepri]

@detiber Do you have an example for the string format?

[detiber]

https://github.com/kubernetes/kubernetes/blob/30ed3b41b7b080cf37639371726a445032d5ef29/pkg/cloudprovider/providers/aws/instances.go#L48-L53

[vincepri]

Could we copy the ProviderID from the Node object now that we're setting the reference?

[detiber]

@vincepri as long as we can query Node objects that belong to a remote k8s cluster, since the management cluster may not be local.

[ncdc]

Depends on https://github.com/kubernetes-sigs/cluster-api/issues/520

[ncdc]

We could consider bumping this to Next if it comes down to the wire - we don't lose any functionality if the data is not populated.

[detiber]

/assign
/lifecycle active