Pig is not running in mapreduce mood (hadoop 3.1.1 + pig 0.17.0)
Part of the problem is that Pig 0.17 doesn't support Hadoop 3 yet.
The Apache Pig Releases states for 0.17:
19 June, 2017: release 0.17.0 available
The highlights of this release is the introduction of Pig on Spark
Note:This release works with Hadoop 2.X (above 2.7.x)
And JIRA PIG-5253 - Pig Hadoop 3 support is still in progress.