Add /etc/ld.so.conf so the dynamic loader has a path even if LD_LIBRARY_PATH is not set

In Akaros, if LD_LIBRARY_PATH is not set, then no .so's will be found. This breaks
a Go test which resets the environment.

Or if you
unset LD_LIBRARY_PATH
you can never run another dynamically linked command.

So put /lib into /etc/ld.so.conf; this gets us past one part of the
os/exec benchmark.

This is ugly but workable. It's disappointing to bring this kind of ugliness into
Akaros but so it goes.

Signed-off-by: Ronald G. Minnich <rminnich@gmail.com>