Prevent AsyncTask from creating too many threads

Bug #10228005

From the ThreadPoolExecutor documentation:

  - If fewer than corePoolSize threads are running, the Executor
    always prefers adding a new thread rather than queuing.
  - If corePoolSize or more threads are running, the Executor
    always prefers queuing a request rather than adding a new thread.
  - If a request cannot be queued, a new thread is created unless
    this would exceed maximumPoolSize, in which case, the task will
    be rejected.

Before this change AsyncTask could create up to 128 threads because
of the limited queue of 10 items (the capacity of a blocking queue
is fixed.)

This change increases the size of the queue to 128 items and reduces
the maximum number of threads to the number of CPU cores * 2 + 1.
Apps can still submit the same number of tasks.

Change-Id: I015d77b53b6a9fda39c618830b34d45a10de5571