code: function getSnapshotsKeys(machineName, versionKey, instanceKey){
  
          let manifest = getManifest();
  
          let machine = manifest.machines[machineName];
          if (!machine) {
              throw new Error("Machine does not exists");
          }
  
          let version = machine.versions[versionKey];
          if (!version) {
              throw new Error("Version does not exists");
          }
  
          let instance = version.instances[instanceKey];
          if (!instance) {
              throw new Error("Instance does not exists");
          }
  
          return Object.keys(instance.snapshots);
      }
docs: Gets the keys of all of the snapshots of the instance of a version of the machine in the repository
  @method getSnapshotsKeys
  @param {String} machineName The name of the machine to get the snapshots's keys
  @param {String} versionKey The key of the version to get the snapshots's keys
  @param {String} instanceKey The key of the instance to get the snapshot's keys
  @returns {Array} An array with all the snapshot's keys of the instance