use --source-path instead of --module-source-path

[homberghp]

fixes #1181 [MJAVADOC-806]

The options file generated uses --module-source-path with the source directory only.
This creates 2 issues:

• the --module-source-path is not considered by the javadoc cli tool for extra doc files.
• the parameter lacks the additional source directory specified in the pom, for doc-files, like below.

 <javadocDirectory>${basedir}/src/main/docs</javadocDirectory>

When feeding the corrected options file to the maven generated javadoc.sh script, it works as expected.

Following this checklist to help us incorporate your
contribution quickly and easily:

• Your pull request should address just one issue, without pulling in other changes.
• Write a pull request description that is detailed enough to understand what the pull request does, how, and why.
• Each commit in the pull request should have a meaningful subject line and body.
  Note that commits might be squashed by a maintainer on merge.
• Write unit tests that match behavioral changes, where the tests fail if the changes to the runtime are not applied.
  This may not always be possible but is a best-practice.
• Run mvn verify to make sure basic checks pass.
  A more thorough check will be performed on your pull request automatically.
• You have run the integration tests successfully (mvn -Prun-its verify).

If your pull request is about ~20 lines of code you don't need to sign an
Individual Contributor License Agreement if you are unsure
please ask on the developers list.

To make clear that you license your contribution under
the Apache License Version 2.0, January 2004
you have to acknowledge this by using the following check-box.

• I hereby declare this contribution to be licenced under the Apache License Version 2.0, January 2004
• In any other case, please file an Apache Individual Contributor License Agreement.