Generate token for controllers

[tamalsaha]

We create predefined service accounts for

• Policy controller appscode:vault:policy-manager
• DB User Manager controller appscode:vault:db-manager

Then create policy necessary for these controllers and associate them with the service accounts using the root token.

Then individual controllers can use those service accounts to talk to Vault and perform operations.

[tamalsaha]

• https://kubernetes.slack.com/archives/C0EN96KUY/p1536960558000100

Each control loop uses the respective service account to run
See https://github.com/kubernetes/kubernetes/blob/master/pkg/controller/client_builder.go#L108 for where the controller manager sets up the service account and credentialed client config
See calls to ClientOrDie for where it is used

[tamalsaha]

Necessary classes copied into https://github.com/appscode/kutil/tree/master/tools/controller

[tamalsaha]

Done.