adding H2 + connection pool support  by rejeevs

git-svn-id: https://svn.wso2.org/repos/wso2/carbon/platform/trunk@177677 a5903396-d722-0410-b921-86c7d4935375
Committing message store improvements.

git-svn-id: https://svn.wso2.org/repos/wso2/carbon/platform/trunk@177678 a5903396-d722-0410-b921-86c7d4935375