Obtain SCL roots by parsing Java conf files

Recently SCL Java config directories were changed from:
    /opt/<vendor>/<scl>/root/etc/java/
to:
    /etc/opt/<vendor>/<scl>/java/
This change breaks existing code.

To make the code work with more scenarios, getSCLRoots() was rewritten
to have less assumptions on file system layout and instead parse
locations of SCL roots directly from Java configuration files
(/etc/java/java.conf).
Add support for installing into SCL root