OAK-2010 - BlobGcMaxAgeInSecs is set to high for MongoBlobStore

Blob GC age is in seconds so convert hours to seconds. Applying patch from Przemo Pakulski Thanks!

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1614807 13f79535-47bb-0310-9956-ffa450edef68