OAK-1888 - provide better feedback when benchmark arguments are missing

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1602201 13f79535-47bb-0310-9956-ffa450edef68
OAK-1877: Hourly async reindexing on an idle instance
 - added null check to comply with the #release apis, and prevent an eventual NPE

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1602207 13f79535-47bb-0310-9956-ffa450edef68