Ozone: Ozone data placement is not even

On a machine with 3 data disks, Ozone keeps on picking the same disk to place all containers. Looks like we have a bug in the round robin selection of disks.

Steps to Reproduce:
1. Install an Ozone cluster.
2. Make sure that datanodes have more than one disk.
3. Run corona few times, each run creates more containers.
4. Login into the data node.
5. Run a command like tree or ls -R /data or independently verify each location.