RFR: 8260289: Unable to customize module lists after change JDK-8258411 [v2]

[Andrew Leonard]

> A problem was found downstream with Eclipse OpenJ9 builds whereby since JDK-8258411 they were unable to extend the module lists.
> This PR adds a IncludeCustomExtension to the conf/module-loader-map.conf, to enable the module list extension again.
> 
> Signed-off-by: Andrew Leonard <anleonar at redhat.com>

Andrew Leonard has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR. The pull request contains one new commit since the last revision:

  8260289: Unable to customize module lists after change JDK-8258411
  
  Signed-off-by: Andrew Leonard <anleonar at redhat.com>

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/2219/files
  - new: https://git.openjdk.java.net/jdk/pull/2219/files/0250fdcc..ffd53bff

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=2219&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=2219&range=00-01

  Stats: 14 lines in 2 files changed: 5 ins; 7 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2219.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2219/head:pull/2219

PR: https://git.openjdk.java.net/jdk/pull/2219