OAK-672: Avoid JCR APIs calling other JCR APIs
OAK-662: Reduce boilerplate code in JCR impl methods
 refactor session related methods to use common base class of SessionOperation, which takes care of establishing session preconditions.

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1461135 13f79535-47bb-0310-9956-ffa450edef68