AccountManagerImpl: Fix method to check and return systemuser, spring injection failsafe

Signed-off-by: Rohit Yadav <bhaisaab@apache.org>

server/src/com/cloud/user/AccountManagerImpl.java

@@ -262,6 +262,9 @@ public class AccountManagerImpl implements AccountManager, AccountService, Manag
 
     @Override
     public UserVO getSystemUser() {
+        if (_systemUser == null) {
+            _systemUser = _userDao.findById(User.UID_SYSTEM);
+        }
         return _systemUser;
     }