plugin-manager: fails to launch multiple plugins using the same driver

[jrasell]

Currently way the config is generated in plugin manager utils does not allow for multiple plugins of the same driver to be launched and results in the last passed winning. An operator may wish to launch the same plugin multiple times for various reasons, including offering the use of multiple running APMs under a single autoscaler.

config:

apm "apm-1" {
  driver = "nomad-apm"
}

apm "apm-2" {
  driver = "nomad-apm"
}