Some .so files have a rpath where to look for the needed .so. When tracing
package dependencies we also have a look there.

This should fix problem when the .so is not in standard location, /usr/lib
or /lib. (for example freeradius plugins)

While here we also reorganize things so we only call apk info --who-owns
once for each package instead of once for each needed .so. This should
speed up things when there are many needed .so files.