Fix: Tests: missing stream redirect causes test failure

Fix: Tests: missing stream redirect causes test failure

The following commit enforced the use of options (instead of arguments)
in the `gen-ust-events` test application:
  commit 6c4a91d639747f260ab46decebc50998ef063712
  Author: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
  Date:   Mon Aug 26 14:22:06 2019 -0400

      tests: gen-ust-events: use options instead of arguments

This makes tests exit (and abort since commit 56d4838) when arguments
are passed to the test application. It currently fails with the
following error:
  ./gen-ust-events -i 32 -w 21 \
    --sync-after-first-event /tmp/allo.hi \
    --sync-before-last-event /tmp/allo.bye /dev/null
  Error: takes long options only.
  zsh: abort (core dumped)  ./gen-ust-events -i 32 -w 21 --sync-after-first-event /tmp/allo.hi

The `/dev/null` at the end of the command line is not associated with an
option so it triggers the sanity check. The `/dev/null` most probably
meant to redirect STDOUT to `/dev/null`.

This commit adds the missing `>` so to overcome the sanity check
problem.

Signed-off-by: Francis Deslauriers <francis.deslauriers@efficios.com>
Change-Id: I3e4d4066079055a542438a63ef4df5c5c4c080cf
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>