Add support for Tez to MagicS3GuardCommitter

The MagicS3GuardCommitter assumes that the JobID of the task is the same as that of the job's application master when writing/reading the .pendingset file. This assumption is not valid when running with Tez, which creates slightly different JobIDs for tasks and the application master.

While the MagicS3GuardCommitter is intended only for MRv2, it mostly works fine with an MRv1 wrapper with Hive/Pig (with some minor changes to Hive) run in MR mode. This issue only crops up when running queries with the Tez execution engine. I can upload a patch to Hive 3.1 to reproduce this error on EMR if needed.

Fixing this will probably require work from both Tez and Hadoop, wanted to start a discussion here so we can figure out how exactly we go about this.