Alternative for managing task array status in Google Batch

[jorgee]

This PR is an alternative to process task status in task arrays.
In the current status, every time that getTaskState is called, we perform two calls to the Google Batch client, one to retrieve the list of tasks(listTasks) and another to get the task state (getTaskStatus). This second call is problematic because it generates the NotFoundException and it is also redundant because the first call already provides the task descriptions including their states.

The BatchClient has a HashMap as a cache of array task status. A new method is created to retrieve the status of a task belonging to a task array. Instead of making the call to the Google Batch API, it checks the status in the cache. When the status is not in the cache or is outdated, the listTasks method is called to update all the array tasks statuses. So, the rest of the array tasks do not require querying the Google Batch API again.

When there is no task status, it returns null and fallbacks to the getJobStatus. This is the same as we were doing when no tasks were retrieved from the job or there was a NotFoundException.

The invalidation time is 1 second because it is the same as the one in GoogleBatchTaskHandler. Another alternative is setting it with the same value as the polling interval.