overloading isroleexist

git-svn-id: https://svn.wso2.org/repos/wso2/carbon/kernel/trunk@178018 a5903396-d722-0410-b921-86c7d4935375
overloading the isexistingrole method

git-svn-id: https://svn.wso2.org/repos/wso2/carbon/kernel/trunk@178019 a5903396-d722-0410-b921-86c7d4935375
updating to match user core

git-svn-id: https://svn.wso2.org/repos/wso2/carbon/kernel/trunk@178020 a5903396-d722-0410-b921-86c7d4935375