Add ROV - The licode tool for inspection and app-level stats

[lodoyun]

Description

This PR implements ROV - a way to inspect licode components and gathering app-level stats for prometheus.
This works by allowing running remote REPL sessions in all erizo server-side components (erizoController, erizoAgent and erizoJS). The main components are:

• RovReplManager: It runs on every erizo component and allows remote REPL sessions to be run via rabbitmq.
• RovClient: The client for RovReplManager. It can start remote repl sessions and run commands in them.
• Inspector: It's a local Repl server that allows using rovClient directly.
• Metrics:
  • RovMetricsGatherer: Gathers all metrics by issuing Rov Commands and processing them
  • RovMetricsServer: Sets up prometheus-client that can be used by a prometheus server to get the metrics from RovMetricsGatherer.

[] It needs and includes Unit Tests

Changes in Client or Server public APIs

[] It includes documentation for these changes in /doc.

[jcague]

I really like this new component!

I left some comments, mostly related to an alternative use of Promises, but feel free to ignore them if they don't make sense.

Also, I'm not sure if using ROV instead of rov for the folder name follows our current naming convention for folder and so on, since we have lots of them in small case. But it's up to you.

[jcague]

do you want to enable logs for UTs?

[lodoyun]

No, I just needed global.config to be present correctly for the ROV componets, otherwise tests will fail. I noticed that's what we did for erizoController and ErizoJS so I followed that pattern.

[jcague]

consider something like:

this._establishComponentConnections(this.components.erizoAgents).then(() => {
  ...
  return Promise.all(erizoListPromises);
}).then((erizoResults) => {
  ...
  resolve();
}).catch(() => {
  ...
});

[jcague]

consider something like:

runInComponentList(command, componentList) {
  return this.connectToComponentList(componentList).then(() => {
    ...
    return Promise.all(runPromises);
  });
}

[jcague]

consider:

connectToComponentList(componentList) {
  ...
  return Promise.all(connectPromises);
}

[jcague]

consider:

connectToSession(componentId) {
  ...
  if (this.sessions.has(componentId)) {
    return Promise.resolve();
  }
  ...
  return rovConnection.connect().then(() => {
    ...
    return Promise.resolve();
  });
}

[jcague]

consider:

closeAllSessions() {
  ...
  return Promise.all(closePromises).then() => {
    ...
    return Promise.resolve();
  });
}

[jcague]

consider:

getTotalRooms() {
  ...
  return this.rovClient.runInComponentList(...).then((result) => {
    ...
    return Promise.resolve();
  });
}

[jcague]

consider something similar to what I propose for getTotalRooms()

[jcague]

you can just return Promise.resolve() here if you want to give it a Promise-like interface.

[jcague]

there is an alternative way, similar to what I proposed before.