Tons of "javac: invalid target release: 1.8" failures happen on YARN precommit runs

[Wangda Tan]

Hi YARN-dev/Common-dev,

I noticed lots of "javac: invalid target release: 1.8" failures happen on
YARN precommit runs since yesterday, not sure if other projects like HDFS
face the same issue.

Filed HADOOP-13167 to track the issue.

Thanks,
Wangda