RFR: 8280868: LineBodyHandlerTest.java creates and discards too many clients

[Daniel Fuchs]

Please find enclosed a simple test fix for:
8280868: LineBodyHandlerTest.java creates and discards too many clients

The LineBodyHandlerTest.java creates and discards many clients (64).
The test has been observed failing intermittently on some systems (Windows 10) while trying to open the client's selector, apparently due to some connection limit.

It seems that using a single client reduces the occurrences in which the test fails.

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Commit messages:
 - 8280868: LineBodyHandlerTest.java creates and discards too many clients

Changes: https://git.openjdk.java.net/jdk/pull/7263/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7263&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8280868
  Stats: 23 lines in 1 file changed: 19 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7263.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7263/head:pull/7263

PR: https://git.openjdk.java.net/jdk/pull/7263