[SPARK-21188][CORE] releaseAllLocksForTask should synchronize the whole method

## What changes were proposed in this pull request?

Since the objects `readLocksByTask`, `writeLocksByTask` and `info`s are coupled and supposed to be modified by other threads concurrently, all the read and writes of them in the method `releaseAllLocksForTask` should be protected by a single synchronized block like other similar methods.

## How was this patch tested?

existing tests

Author: Feng Liu <fengliu@databricks.com>

Closes #18400 from liufengdb/synchronize.