OPENDJ-2741 Fix maven default lifecycle

The maven default lifecycle build-phases from generate-sources to prepare-package (included)
were broken on the server build because of the following reasons:
* maven-plugin:generate-config expected a jar file to browse XML
descriptors and get a folder instead.
The fix consists to take in account the use case when the URL returned is actually a local folder path.

Once that fixed, we got another error which was related to the maven-dependency-plugin issue MDEP-187.
The maven-dependency-plugin:unpack goal only works for build phase >= package for multi modules projects.
Remove the use of the plugin to address the problem by directly pointing to the local path of:
* opendj-legacy sources
* opendj-maven-plugin xml configuration reference files