code: public OperationFuture<List<Server>> createSnapshot(Integer expirationDays, Server... serverRefs) {
          return powerOperationResponse(
              Arrays.asList(serverRefs),
              "Create Snapshot",
              client.createSnapshot(
                  new CreateSnapshotRequest()
                      .snapshotExpirationDays(expirationDays)
                      .serverIds(ids(serverRefs))
              )
          );
      }
docs: Create snapshot of a single server or group of servers
  
  @param expirationDays expiration days (must be between 1 and 10)
  @param serverRefs     server references list
  @return OperationFuture wrapper for BaseServerResponse list