RFR: 8278166: java/nio/channels/Channels/TransferTo.java timed out

[Brian Burkhalter]

In the `testMoreThanTwoGB()` sub-test, only fill the last section of the file with random data in order to reduce test execution time.

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Commit messages:
 - 8278166: java/nio/channels/Channels/TransferTo.java timed out

Changes: https://git.openjdk.java.net/jdk/pull/6707/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6707&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8278166
  Stats: 20 lines in 1 file changed: 16 ins; 1 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6707.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6707/head:pull/6707

PR: https://git.openjdk.java.net/jdk/pull/6707