[SPARK-19796][CORE] Fix serialization of long property values in TaskDescription

## What changes were proposed in this pull request?

The properties that are serialized with a TaskDescription can have very long values (eg. "spark.job.description" which is set to the full sql statement with the thrift-server).  DataOutputStream.writeUTF() does not work well for long strings, so this changes the way those values are serialized to handle longer strings.

## How was this patch tested?

Updated existing unit test to reproduce the issue.  All unit tests via jenkins.

Author: Imran Rashid <irashid@cloudera.com>

Closes #17140 from squito/SPARK-19796.