support busybox for manual trace tests

The busybox version of find does not support using -L, and it does not
appear to be needed in order to pass the test.  In the interest of
being able to run internal UST tests on a busybox based rootfs,
appropriately detect if -L is available as an argument to find and use
it when it is available.

Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
Signed-off-by: Nils Carlson <nils.carlson@ericsson.com>