Add ability to override basedir and package type for oracle java

[fraenki]

This is a resubmission of #298, because it looks like the original submitter lost interest.
In addition this fixes several small issues of the original submission:

• fix tests (the Exec was missing the full version information)
• use evaluated/os-dependent paths from $_basedir instead of hardcoded values

ping @david22swan

[david22swan]

[david22swan]

@fraenki All looks good to me, thanks for putting in the work to get this finished. :)