Support running multiple manager per host in accumulo-cluster script

[keith-turner]

Is your feature request related to a problem? Please describe.

The accumulo cluster script does not support running multiple manager per host.

Describe the solution you'd like

Change cluster.yaml and the scripts to support something like the following.

manager:
  servers_per_host: 2
  hosts:
    - localhost

Additional context

Can currently run multiple managers on a single host w/ the following command.

ACCUMULO_CLUSTER_ARG=5 accumulo-service manager start