Introduce the concept of shared targets

[manugarg]

We could do it in two ways:
a) Define targets independently of the probes and assign each one of them a unique id. Then in the probe definition refer to that id.

targets {
  id: "vm-private-ip"
  gce_targets {
  }
}

probe {
  name: "vm-to-vm"
  type: PING
  targets_id: "vm-private-ip"
  ping_probe {
  }
}

b) Introduce the concept of probeset where a probeset is a set of probes that use the same targets.

probeset {
  targets {
    ..
  }
  probe {}
  probe {}
}

[manugarg]

This has been implemented: 4ad6ea2

Available in versions - v0.10.5+.