CRAS: test_client - add --help.
CRAS: test_client - add --help.

Adds --help to list the possible arguments.

BUG=none.
TEST='cras_test_client --help'

Change-Id: I549ad82e59406b3077035151325aa494666c0f46
Signed-off-by: Dylan Reid <c791bfe44996c1eed9c7149a0c5f12a86d58eb85@chromium.org>

drinkcat/adhd,drinkcat/adhd,drinkcat/adhd,drinkcat/adhd,drinkcat/adhd,drinkcat/adhd