RFR: 8269692: sun.net.httpserver.ServerImpl::createContext should throw IAE [v2]

[Julia Boes]

> `com.sun.net.httpserver.HttpServer::createContext` specifies `IllegalArgumentException` to be thrown if a context already exists for the path provided. The implementation class`sun.net.httpserver.ServerImpl` does not comply with this, which is fixed by this change.
> 
> Testing: Tier 1-3 all clear.

Julia Boes has updated the pull request incrementally with one additional commit since the last revision:

  address PR comments

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/4665/files
  - new: https://git.openjdk.java.net/jdk/pull/4665/files/bc211450..80c856b1

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=4665&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=4665&range=00-01

  Stats: 17 lines in 2 files changed: 14 ins; 2 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4665.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4665/head:pull/4665

PR: https://git.openjdk.java.net/jdk/pull/4665