libpython3.so is the "ABI compatible" wrapper library around
libpython3.5m.so - it is not actually used by anything in LO right now,
but let's ensure it has RPATH $ORIGIN just in case.

This revealed that the AIX patch in python3 accidentally changed the
SONAME of libpython3.5m.so from upstream's libpython3.5m.so.1.0
on ELF platforms, because the SONAME variable was set in the shell
command but read as a make variable in the next line, which is actually
evaluated earlier.

So rename a few files in packages to use the upstream SONAME.

Change-Id: I3611f75eee62b0993b853230521a2fa41ac5cd9c