Add PUT Copy operation to CS driver

Riak CS supports PUT Copy API at version 1.5.
This PR adds the API call to CS driver `basho_bench_driver_cs`.

Completely orthogonal but this PR also includes automatic user/bucket creation.
By configuring Riak CS as `admin_auth_enabled=false`,
CS driver can run without setting access key and secret key.
It creates an user (if necessary), retrieve the user information and create a bucket (if necessary).
If access key and secret key are set by a config, then the driver runs as before.