RFR: 8278398: jwebserver: Add test to confirm maximum request time

[Julia Boes]

This new test confirms that the jwebserver does not wait indefinitely for a request to arrive, but instead closes the connection when the maximum request time is reached. To facilitate this, Exchange::run is amended to process cancelled keys in the case where the current thread is the dispatcher thread (which is the case for the jwebserver).

Testing: tier 1-3 all clear.

-------------

Commit messages:
 - Merge branch 'master' into 8278398
 - initial commit

Changes: https://git.openjdk.java.net/jdk/pull/7052/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7052&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8278398
  Stats: 219 lines in 2 files changed: 218 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7052.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7052/head:pull/7052

PR: https://git.openjdk.java.net/jdk/pull/7052