test: update LD_LIBRARY_PATH more often

Running rootdev might work if the shared lib is installed in the
current system, so add it to the library path if the lib exists.

BUG=None
TEST=`./rootdev_test.sh` still works

Change-Id: I3c3533ae050d8e793f68dcc7a2338d2ddc6a86a2
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/rootdev/+/5554960
Reviewed-by: Brian Norris <briannorris@chromium.org>
Auto-Submit: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Brian Norris <briannorris@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
1 file changed