Changes

releng: align javadoc sections in parent pom.xml file

With this both commands yield the same result:
- mvn compile javadoc:aggregate
- mvn compile javadoc:aggregate -Pbuild-api-docs

Also, exclude btf and rcp from javadoc.

Change-Id: I2d9c68924dc4e743d09b132925cb575109f9267e
Signed-off-by: Bernd Hufmann <bernd.hufmann@ericsson.com>