CBQE-0: improve logs in log_command_output with track_words

Change-Id: Icab00362be184fb14ecdf16360f745793994dc01
Reviewed-on: http://review.couchbase.org/35069
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>
Tested-by: Andrei Baranouski <andrei.baranouski@gmail.com>