Add client role

The client role is responsible for provisioning the users, databases
and privileges. It is required when running InfluxDB in a container
because the deployment of InfluxDB and the provisioning phase are
decoupled. Non-containerized deployments are left unchanged with the
provisioning managed by the server state.

Change-Id: I7c9a05f2109f76aadf84953374c740a865d59106
7 files changed