[SPARK-3347] [yarn] Fix yarn-alpha compilation.

Missing import. Oops.

Author: Marcelo Vanzin <vanzin@cloudera.com>

Closes #2236 from vanzin/SPARK-3347 and squashes the following commits:

594fc39 [Marcelo Vanzin] [SPARK-3347] [yarn] Fix yarn-alpha compilation.
SPARK-3052. Misleading and spurious FileSystem closed errors whenever a ...

...job fails while reading from Hadoop

Author: Sandy Ryza <sandy@cloudera.com>

Closes #1956 from sryza/sandy-spark-3052 and squashes the following commits:

815813a [Sandy Ryza] SPARK-3052. Misleading and spurious FileSystem closed errors whenever a job fails while reading from Hadoop