Refactor testcases that use rpc_client to restart the node using node spawner.

[ermineJose]

The testcase currently creates a network using antctl, with rpc enabled in nodes, as the rpc is being removed by metric_service, the restart support cannot be provided with metric_service.

As a work around, replace the local network created by antctl with network spawner utility, where the nodes are run as threads instead of services. This way, we can restart the nodes within the testcase itself, avoiding the dependency on rpc inside nodes. this can unblock the metric_service PR.