RFR: 8278469: Test java/nio/channels/FileChannel/LargeGatheringWrite.java times out

[Brian Burkhalter]

Modify test directives so that `LargeGatheringWrite` and `MapTest` in `java/nio/channels/FileChannel` are not run concurrently with other tests.

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Commit messages:
 - 8278469: Test java/nio/channels/FileChannel/LargeGatheringWrite.java times out

Changes: https://git.openjdk.org/jdk/pull/9416/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9416&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8278469
  Stats: 2 lines in 3 files changed: 1 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/9416.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9416/head:pull/9416

PR: https://git.openjdk.org/jdk/pull/9416