Setting default subDomain if a subDomain has not been specified for the member

git-svn-id: https://svn.wso2.org/repos/wso2/carbon/kernel/trunk@181419 a5903396-d722-0410-b921-86c7d4935375
fix for user name null issue in carbon context

git-svn-id: https://svn.wso2.org/repos/wso2/carbon/kernel/trunk@181420 a5903396-d722-0410-b921-86c7d4935375