log: fix help for --qi-log-context ("Date" missing)

Change-Id: I503692af4893392da1133612603a9b3d6d4d4bb5
Reviewed-on: http://gerrit.aldebaran.lan/23024
Reviewed-by: gjacob <gjacob@aldebaran-robotics.com>
Tested-by: gerrit
Reviewed-by: cgestes <gestes@aldebaran-robotics.com>