We don't call klog.InitFlags yet, because that will cause a flag
redefinition error until we get everyone to stop using glog. That
will happen when we update to k8s 1.13.
We've done this in the API already, but we had a single CAStore
interface that did Keysets and SSHCredentials. Separate out
SSHCredentials into SSHCredentialStore, and start using API objects as
our primary representation.