save CA as secret

[deitch]

Fixes #10

Instead of keeping the CA key/certificate as something statically stored in cluster.yaml, this does the following:

• stores it as a kubernetes secret
• makes the secret part of provider-components.yaml so that it is pivoted correctly to a new cluster (if using an ephemeral bootstrap cluster)
• machine actuator consumes that secret
• cluster actuator consumes that secret and, if blank, generates and stores a new one in that secret (to be used later by machine actuator)
• lets the user set the path to the key and certificate files in generate-yaml.sh

[deitch]

Note that this breaks clusterctl. We have to live with it until we switch to v1alpha3

[matoszz]

@deitch sorry for the delay - LGTM